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The Solar System
History of discovery
The Sun and Moon, and the planets Mercury, Venus, Mars, Jupiter, and Saturn were known to the ancients, all believed to be orbiting the stationary Earth. Their paths were refined to Ptolemy's elegant mathematics for two millennia until this was overturned in 1543 by Copernicus' De Revolutionibus Orbium Caelestium, which was confirmed in 1610 when Galileo discovered four satellites of Jupiter: Io, Europa, Ganymede, and Callisto, which have since been called the Galilean satellites. Europa was named by Simon Marieu, who spotted the satellites the very next evening after Galileo.
In 1596, Tycho Brahe's assistant Johannes Kepler, because of deviations he observed in the orbit of Mars, wrote: Inter Jovem et Martem interposui planetem (Between Jupiter and Mars I have placed a planet), thus anticipating the Titius-Bode empirical "law" which came more than a century later.
The discovery of Jupiter's satellites triggered the search for others, and as Jupiter had already been covered by Galileo, the search was concentrated on the next biggest planet, Saturn, whose largest satellite, Titan, was discovered in 1665 by the Dutch astronomer, Christian Huygens. The first Cassini of the Paris Observatory found Iapetus in 1671, Rhea in 1672, and Tethys and Dione in 1694, giving Saturn five satellites.
Robert Hooke reported Jupiter's Great Red Spot in 1664, and it has persisted ever since, with many discussions about its origin, which still go on. The Voyager satellites have photographed several smaller” red spots” on Jupiter.
In 1766, Titius von Wittenburg drew attention to the regular empirical relationship of the solar distances of Venus, Earth, and Mars, then a gap, then Jupiter and Saturn; Johann Bode predicted a planet in this gap, was indeed Kepler had done more than a century before on quite different grounds.
This empirical relationship was taken much more seriously when William Herschel discovered Uranus beyond Jupiter and Saturn, still in accordance with Bode's rule. Then the hunt was on for the missing planet between Mars and Jupiter. The Hungarian Baron Franz X. von Zach organized the group of searchers, who called themselves the celestial police.
Meanwhile, in 1787, Herschel found that, like Jupiter and Saturn, Uranus also has satellites, Titania and Oberon, and two years later he added Enceladus and Mimas to Saturn. Being small and close to Saturn's bright rings, Mimas was difficult to observe from Earth, until Voyager I passed within 88,000 km and recorded detail down to 2 km, and found that Mimas is cratered to saturation, the largest being Arthur (called after the legendary king), 130 km in diameter and 10 km deep with a 6 km central peak.
On the first of January 1801, Guiseppi Piazzi, an Italian monk and Director of the Palermo Observatory, found Ceres, the first asteroid, and followed her for many days, lost her, and recovered her. It was a young mathematician, Karl Friedrich Gauss, who first calculated the details of Ceres' orbit.
Soon afterward, Pallas was found, then Juno, sarcastically scorned by Gauss as ”a couple of clods in the sky” where Olbers had predicted a new planet. It is a pity that Herschel named them ”asteroids” to indicate that they were mere points of light which could not be resolved in a telescope. ”Planetoids” would have been a better name, because they are planet-like not star-like.
Bond discovered Saturn's Hyperion in 1848, and Lassell, who had found Neptune's Triton in 1846, followed with Ariel and Umbriel around Uranus in 1851. Johannes Kepler had predicted two moons for Mars, and Asaph Hall found them in 1887, naming them Phobos (fear) and Deimos (terror) as they were the attendants of Mars, the god of war.
Both of them had been described by Jonathan Swift in his novel Gulliver's Travels published in 1726, with good estimates of their sizes and orbital distances seemingly half a century before they were discovered! How is that possible?
It seems that Dutch opticians who had already made telescopes, had previously observed and reported Mars' satellites, but had been ridiculed and not believed, the common fate of discoveries contrary to accepted dogma.
Jupiter's Amalthea, only 113 thousand km from his surface, was discovered by Barnard in 1882 and named after the nymph who nursed Jupiter.
Maximillian Wolf, Director of the Konigstuhl Observatory of Heidelberg, in 1891 commenced the photographic search for asteroids and added 231 new ones to the growing list. In 1906 he discovered the first Trojan asteroid stable in Jupiter's orbit. Pickering, of Harvard Observatory, found Saturn's Phoebe in 1898.
For Jupiter, Perrine discovered Himalia (1904) and Elara (1905), Melotte discovered Jupiter's retrograde Persiphae in 1908, and Nicholson discovered Sinope (1914), prograde Lysithea and retrograde Carme (1938), and Ananke (1951 ).
In 1948 Gerard Kuiper discovered Uranus' Miranda, and in 1949 Nereid and Pluto's Charon. In Greek mythology, Charon ferried sinners across the river Styx to Hades, the Underworld ruled by Pluto. Voyager I added three more small satellites to Jupiter in 1979, and six more satellites for Saturn, and Pioneer II added another two.
In 1974, Charles Kowai discovered Jupiter's Leda, whom he named after the mythological mother of Castor and Pollux, and in 1977 found an enigmatic body between the orbits of Saturn and Uranus, which he named Chiron, son of Saturn and grandson of Uranus. Chiron is in the size range of asteroids, although farther out than any other asteroid, so was first listed as asteroid 2060.
Chiron's orbit inclination is 17o, surface temperature varies from 60oK at aphelion to 90oK at perihelion; its brightness fluctuates as it rotates with a period of nearly six hours, which is within the range of either comets or asteroids. Chiron is larger than any other known comet, seemed to lack a comet's coma or tail, and its orbit was unusual for a comet as it was just inside Saturn's orbit at perihelion (8.5 AU) and just inside Uranus's at aphelion (19.2). However, as Chiron approached perihelion it developed a coma at least 130,000 km across.
So Chiron is really a comet, the largest so far known, and unusual in not closely rounding the Sun. Iteration of Chiron's orbit suggests that in due course it will approach Saturn closely, so that its orbit will then be reset.
In a gross view, the solar system is a Sun Jupiter binary. Jupiter orbits the mass-center of the solar system in 11.8 years, and Sun to balance this large mass, also orbits the mass center of the solar system in approximately I I.8 years (hence the sunspot cycle). Jupiter contains more matter than that of all the other planets combined, and Jupiter and the Sun are similar chemically, mainly four parts hydrogen and one part helium.
The solar system is bimodal. The Earthly group, Mercury, Venus, Earth, Mars, and perhaps Moon - small, dense, silicate bodies, with no rings and no satellites (except Deimos and Phobos - probable captured asteroids) - contrast with the great planets, Jupiter, Saturn, Uranus, and Neptune - large, gaseous, much less dense, with several rings, and many satellites.
Orthodox astronomy interprets this simply as condensation temperatures in a sequence away from the Sun, but why bimodal, rather than a gradient? After all, there is a wide gradient of condensation temperatures of water, C02, NH4, CH4, and N2, and of their freezing points.
Immanuel Kant suggested that a collision between the Sun and another star had produced the solar system. Chamberlain and Moulton suggested the tidal disturbance by the close passage of another star, developed by Jeans, later changed by Jeffreys to a glancing contact. But none of such dualistic encounter theories has survived close scrutiny, so there has latterly been a search for a monistic theory.
The standard meme is that the solar system originated from the condensation of a cold gas cloud. But as explained in the next chapter on stars, I suggest that the solar system may have been born some four billion years ago as an Antares-type red giant, as a result of a nova explosion of a small star, the proto-Sun.
The mass of the newborn solar system would have been about half the present mass of the Sun, the radius about 500 times the present solar radius, and the surface temperature about 3,000oK, low enough for molecular gas-phase water to be present. In the hotter modern Sun, water is completely dissociated into O and OH radicals, except in the cooler pits of sunspots where molecular water has been recorded.
The pre-solar red-giant stage would seem to explain the anomalies in isotopes of xenon, carbon, and nitrogen in carbon chondrites (Grady and Wright, 1990). The half life of 26Al is only 700,000 years (long since replaced by its stable daughter 26Mg) so it could not have existed for a long period before the birth of the solar system, and must have been produced during the Sun's nova explosion.
As originally proposed by R. A. Lyttleton, there was at least one companion star, whose orbit about the Sun determined the ecliptic plane, the general rotation and orbital sense of most of the subsequent planets and their satellites, and the distribution of angular momentum in the solar system. (The Sun, with 99.9% of the mass of the system has only 0.5% of the angular momentum, which implies a former companion star).
As earthlings, we tend to regard Sun as the paradigm of stars in its class, but Sun, a loner, is not typical. The majority of Sun-like stars are binaries, or in a three or four star gravitational group. I have suggested that a-Centuari may have been the Sun's binary companion after the nova explosion (which could explain the planar ecliptic and the anomalous distribution of angular momentum in the solar system), but such a multiple system would be gravitationally unstable, resulting in the ejection of a-Centauri, which is now at least 35o south of the ecliptic.
Even without ejection by gravitational instability, the proper motion of those stars within range of parallax measurement varies up to 600 km/s, which is more than adequate for the Centauri ternary to move to its present distance from the Sun (4.3 light- years) in the four billion years since the nova. Added to this is the Hubble expansion since that time, which is also nearly this magnitude.
The Centauri group is more than 30o below the ecliptic, even allowing for the circular path the pole traces through the stars by the precession of the equinoxes. So if ejection through gravitational instability cannot explain this discrepancy, we must look elsewhere for the original companion of the proto-Sun. (b-Centauri, the other ”Pointer” , although in the same general direction, is very much more distant and not part of the group).
Hubble expansion of the planetary orbits would also progressively reduce the solar heat received by the Earth, leading to increasing glaciation. However Chin and Stothers (1975) reported the surprising result that” the heat flux reduction through increasing distance is neatly balanced by increasing luminosity” . Other models predicted total freezing of a11 the Archean waters of the-Earth by the reflectivity of the CO2 cirrus-like clouds, and still others predicted quasi-Venusian warming (Kuhn, 1992; Caldeira and Kasting, 1992) but the geologic fact stands - of continuous seas since the Archean.
The Antares-like red-giant stage was brief before the Sun returned to the main sequence. If this were not so, such red giants would be much more numerous, because they are luminous enough to be seen out to great distances.
Collisions between primitive planets during the early evolution of the solar system have been invoked to explain several anomalies, such as Mercury's high density, the Moon's origin and gross impoverishment of volatiles, Venus's very slow retrograde rotation, the alleged disruption of Aztex (a postulated precursor of the asteroids), and the nearly 90o obliquity of Neptune.
According to Ringwood (1986) the Earth was impacted obliquely by a Mars-sized body during the late stage of the accretion of the terrestrial planets, which resulted in the Earth-Moon system. This theory was developed further by Newsom and Taylor (1989), and is currently favored by the establishment.
Every body in the solar system, from the very smallest observed (like Deimos) to the largest with 1000 km craters, establish without doubt that violent collision was rife in the early history of the system, so an early major collision with the Earth is not exceptional. Ringwood and Taylor have shown that the detailed geochemistry of the Moon agrees well with this theory.
The Moon's density is 3.3, the Earth's decompressed density is 4.4, Mercury's is 5.3, so Mercury must have proportionally a larger iron core than the Earth, almost as big as the planet itself, far more than the differential condensation model predicts. Some theorists have suggested that Mercury originally was much larger with a thick silicate mantle, which was boiled off early by impact with a large asteroid.
The chemical composition of the planets has been attributed to their respective distances from the Sun. J.S. Lewis, assuming a simple pressure-temperature adiabatic relationship throughout the primitive nebula (Lewis and Prinn, 1984), showed that at Mercury's orbital distance, sphene, iron, nickel, and olivine would solidify (which would account for Mercury's high density); at the Earth's distance pyroxenes, pyrite, and feldspars would form; at the distance of Mars, Fe0 and amphiboles would form, whereas at the distances of Uranus, Neptune, and Pluto only water ice would solidify.
None of the planets from Mercury to Mars would have retained any of their inert gases, any now present being radiogenic (for example the Earth's argon, derived from radioactive potassium). The planets and their satellites consist of three components, iron, silicate rock, and gases. Mercury, Venus, Earth, Mars, and the asteroids consist of iron and silicates, the outer planets have large proportions of condensable gases.
At the position of Jupiter and his satellites water would be the main ice, but at Saturn's distance, gases such as ammonia, methane, methanol, and nitrogen should have solidified, either as distinct layers, eutectics, intergrowths, or as compounds such as ammonium hydrate (NH3.H2O).
Intergrowths could lead to partial-melt lavas, perhaps with liquid sulfur. At the prevailing temperature gradient from the Sun, the great gas planets should all have solidified completely, but each of them is a net radiator, and has maintained the gaseous condition.
The 58.6 Earth-day rotation period of Mercury with the noon Sun overhead gives a temperature of 723oK (so gases have mostly dissipated) and a midnight temperature of 93oK. Only Venus gets hotter, only Uranus and Neptune colder, and Mercury has no atmosphere to smooth temperatures and no greenhouse gases to retain surface heat.
Venus has a surface temperature 730oK, maintained by thick greenhouse gases and also smoothed longitudinally by the thick atmosphere, despite the planet's slow rotation. the Earth’s surface temperature ranges from an Antarctic extreme of 200oK to a typical desert extreme of 300oK. The difference would be much greater except for latitudinal convective circulation. Longitudinal differences are due to the obliquity of the rotation axis.
The surface temperature on Mars varies from 150oK to 250oK. ”Surface” temperatures in the vicinity of Jupiter and its satellites are in the range of 100o ± 5OoK. Jupiter's temperature ranges up to 160oK, because of heat generated within the planet. Io's surface temperature is 143oK.
Around Saturn the temperature is about 72oK, but for Saturn it is 96oK because Saturn and Jupiter are net radiators, producing more heat than they receive from the Sun. Titan’s surface temperature is 91oK, raised by the greenhouse effect of the thick atmosphere. Chiron, between Uranus and Saturn, ranges from 60oK to 90oK, while Uranus is only 58oK.
Uranus is thought to consist of water-ice with some admixture of methane and ammonia ices, plus hydrogen (partly in metallic phase) and helium in solar proportions. Some magnesium and iron silicates, and minor amounts of CO and H2S, are also probably present.
Constraints, such as mass, mean density, moment of inertia, gravity acceleration, and theoretical models of nebula composition at Uranus' distance from the Sun, have resulted in a model with a rock core of about 0.4 of the mass of the planet, a thicker intermediate layer of ices of water, ammonia, and methane with an average density of 2.5, and a gaseous shell of hydrogen and helium with a thickness of about a quarter of the planetary radius. Other models have smaller rock cores or no rock at all. Uranus is unique in the solar system in that it receives more heat at the poles than the equator, because of the high obliquity.
Neptune's temperature is 58oK; it is a very windy planet, which smooths out latitudinal differences. Andrew Ingersoll reports winds approaching the speed of sound. Neptune's satellite, Triton, has a surface temperature of only 35oK.
As the Pluto-Charon binary overlaps the orbit of Neptune, the average temperature must be about 50oK, in the same general range, which is consistent with the presence of solid methane on the surface in equilibrium with a small amount of methane gas. The orbital eccentricity (0.25) is high, so temperature must vary widely throughout the ”year”.
But size, irrespective of temperature, is also of great significance. In Appendix 1, I have listed in order of their size known bodies of the solar system one kilometer or more in radius, whether they be planets, satellites, asteroids, or comets.
Radius less than 50 km
Bodies less than 50 km radius (and mass less than 1018 kg) are irregular rocks, without sufficient self gravitation to pull themselves toward a spherical shape. They have no atmosphere, no regolith; no volcanism nor tectonic activity, but they do have pock marks from many impacts. Thousands of asteroids are in this size range (see Appendix 1) and most comets.
By good luck rewarding accurate science, a close-up picture was obtained by the Galileo spacecraft of asteroid Gaspra (15x6x7 km radius) an irregular rock. On Galileo's second passage by the asteroid belt, it found that Ida (15x 29 km radii) has its own satellite ”moon” Dactyl some 500 m in radius and 100 km from Ida. Dynamic considerations imply that Ida and Dactyl originated in the same catastrophe which disrupted their parent body.
Of the satellites of planets, there are seven of Jupiter's, Leda (10 km radius), Pan (12 km), Hades (15 km), Adastraea (15x20 km), and Hera (20 km) are in this range. Two of Jupiter's outer prograde satellites, Lysithea (18 km) and Elara (20 km), and also four small outer retrograde satellites, Ananke (3-14 km), Sinope (3x18 km), Carme (4x20 km), and Persiphae (4x20 km), are probably captured asteroids.
Four Saturn satellites, Calypso (11x11x12 km), Telesto (15x10x8 km), Atlas, and 1989 S6, and four others, S 12 ( 17x 16x 15 km), S 13 and S 26 (35x35x65 km) are in this size range; Figure 12 of Reichstein (1985) reveals these to be fragments of larger cratered bodies. Also included are eight Uranian satellites ranging from 20 to 35 km radius, including Corrtelia (~20 km), Ophelia (~25 km), Juliet (29 ± 5), Rosalind (27 ± 4). and Belinda (33 ± 4).
The two satellites of Mars, Deimos, (6x6x8 km) and Phobos (19x21x20 km), are believed to be captured asteroids. Their rotation is synchronous, with their longest axis pointing toward Mars, so that their rotation is about the maximum moment of inertia.
Phobos is inside the Roche limit, where the planet's gravity equals the satellite's self gravity. Phobos has, of course, significant cohesion to hold together and the strong tidal drag will continue to reduce Phobos' orbit, until it breaks up as a ring, or falls into Mars. The orbital revolution of Phobos is shorter than the rotation period of Mars, so that, although it is prograde, seen from Mars, Phobos rises in the west and sets in the east.
Radius 50-100 km
These bodies are still far from spherical shapes. They have no atmosphere, no regolith, no volcanism, and no tectonic activity. Nearly two thousand bodies in this size range, including cigar shaped 1981 N 2 (50x5km); Hestia 67 (also ~ 100 km) and Himalia (85 km), four of Saturn's satellites, Epimetheus (70x50x50 km),1980 S 1 (100x100x95 km),1980 S 3 (70 km), and 1980 S 27 (70x50x40 km), two belonging to Uranus including Puck (75 ± 3 km radius), and three of Neptune's, 1989 N 2 (95 km), 1989 N 3 (90 km), and 1989 N 4 (75 km). They are mere points of reflected light, so little is known about their shape (except that variation during rotation usually indicates non-sphericity).
Radius 100-200 km (1019 kg)
Such bodies still lack atmosphere or sufficient self gravitation to pull themselves into a spherical shape, so reflectivity varies as they rotate, although they are too small and distant for their shapes to be resolved optically.
At least some are binary pairs; the gravity field of this size range is strong enough to hold a partner in stable orbit as distant as 30,000 km. Like Ida (above), Herculina (110 km radius) has a small binary satellite 1000 km away. Near-Earth-asteroid Castalia seems to consist of two bodies orbiting each other as a contact-binary. Chiron between the orbits of Saturn and Uranus was first regarded as asteroid 2060, but now regarded as a Comet.
In this size range there are hundreds of asteroids, including Europa (138 km), Juno (144x115 km radius); two of Jupiter's satellites, Amalthea (45x82x135 km, ~1019 kg) and J 15 (55x95x122 km); there are six satellites of Saturn: Phoebe (110 km radius), S 10 (160 km),1980 S 1 (220 km) and l980 S 3 (140 km) which share the same orbit within the Roche limit, so they may be fragments of a larger satellite that disrupted prior to complete disruption to a ring, and Hyperion (100x120x175 km).
Also Neptune's Proteus (200 km radius) and Nereid ( 160 km) in a highly eccentric orbit (0.749 from 54RN to 400RN). Nereid's brightness varies by a factor of four during rotation, presumably because it is very elongated. Hyperion (100x120x175 km) is a very irregular but heavily cratered body in exact 4/3 resonance with its large neighbour, Titan.
Radius 200-500 km
Mass is here from 1019 to 1020 kg, so a significant threshold is reached where self gravitation is sufficient to draw bodies into a spherical shape. They also begin to show polygonal surface extensional fractures, and the first signs of volcanism, outgassing calderas, and volcanic resurfacing. They have no atmosphere. Most asteroids are smaller, but Pallas and Vesta, both in the lower part of this range, are almost spherical.
Saturn's Mimas, (197 km radius, 1.2 density) is on the threshold of the 200 km cut-off, and it has attained a spherical shape. Mimas is in synchronous rotation with Saturn (it is only just outside the rings), but Mimas appears to lack volcanic ”resurfacing”; it has extensional chasms about 3 km wide, which trend Northeast, North of the equator (for example geta Chasma) and south-east, south of the equator (for example Rangea, Ossa, and Penea Chasmae). A Voyager 1 photograph of Mimas (Reichstein, 1985, Figure 9) shows many craters; the very late Herschell crater is 130 km in diameter, with a 6 km central peak.
Saturn's very bright satellite Enceladus (251 km, 8xl019 kg, density l.l), is spherical, asymmetric in resurfacing and degree of cratering (presumably because it is so close to Saturn and always presents to it the same face). Saturn's E-ring has an increased particle density in the vicinity of Enceladus' orbit. Enceladus has a global through going tensional chasm system and, several quadrate fractures, which appear to be young.
Uranus'Miranda (242 km radius 7.7x1019 kg) has a most prominent global tensional fracture system and rift canyons, which are closely conformable with the extraordinary quadrate blocks (“coronae” , but quite unlike Venus' coronae), which are not matched anywhere else in the solar system and have puzzled planetologists ever since their discovery by Voyager II.
113) has been broken by five radial, major canyon rift zones, between
30 and 40 km wide and 6-8 km deep, radiating roughly from the south pole.
These rift canyons separate five coherent radial blocks Arden, Mantua,
Elsinore, Silicia, and Dunsilane-200-300 km across, with water-ice surface
(viscosity may be lowered by methane or ammonia). Inverness seems to have
been a central block, near the south pole.
Each of the major blocks is patterned with long parallel ridges a couple of kilometers apart and a few hundred meters high, which normally run east-west along the latitudinal small circles, except near the boundaries of Elsinore, Arden, and Inverness, where they faithfully parallel the edges of the blocks for some 80 km inward. I do not know what these ridges are. Arden, Inverness, and Elsinore are much less cratered than the other three blocks, hence they are younger surfaces, following volcanic resurfacing.
Many theories have been offered for Miranda's extraordinary surface pattern. Shoemaker suggested that Miranda shows late accretion” caught in the act” 200 km bodies in process of sinking and assimilation. McKinnon (1988) has reviewed such ”sinker” theories. Miranda is the innermost and smallest of the five large satellites of Uranus, and the gravity pull of the planet must be approaching Miranda's self gravitation, although it is still outside the Roche limit (assuming zero cohesion). So, with the increasing mass of Uranus, Miranda is not far from disintegrating to form a ring even more spectacular than Saturn's.
I suggest that the small difference between Miranda's self-gravitation and Uranus' gravitation may be the explanation of Miranda's extraordinary incipient fragmentation indicated by its coronae.
Miranda has near perfect sphericity. According to orthodox theory, little Miranda should be dead and lifeless, whereas it has certainly been tectonically and volcanically active very recently, and I suggest, continuing now! Is Miranda in the state approaching roche-limit disintegration? The Arden, Inverness, and Elsinore blocks have very few craters, and therefore are young.
But if they are simply dispersed blocks, they should retain their original cratering. There was no wind or water erosion to strip them, so they must have been buried. By what? Resurfacing cryo-volcanism is the suggestion adopted by the NASA interpreters. The one thing that is certain about Miranda is the gross expansion, but on a scale not matched anywhere else in the solar system.
Pallas, 269 km radius, 2x1020 kg mass, 2.6 density, the second asteroid to be discovered (by Olbers in 1802), is in a steeply inclined orbit (237o). Pallas is a carbonaceous chondrite of low albedo (0.062).
Vesta, 277 km radius, 2.7x1020 kg mass, and 3.6±0.5 density, though only half the radius, is much brighter (albedo 0.25) than Ceres (see below), Vesta being the only asteroid visible to the naked eye (magnitude 6). Also Vesta's orbit is much nearer the Sun and hence the Earth (2.2 against 2.8 AU). Its density and spectrum resemble basalt, implying a once molten interior. Vesta has a minimum albedo when her maximum cross section faces the Earth.
Ceres (461 km radius, mass 1.17x1021 kg, density 2.3) the largest asteroid, is spherical within a few percent, which can fit an ellipse of semi-axes 453x479 km with topography as high as 10 km, but nothing is yet known about tectonics. The density and spectrum resemble carbon chondrites, hence she is much duller than smaller Vesta.
Radius 500-1000 km
With a mass from 1020 to 1021 kg, all bodies have a spherical shape, tensional fracture patterns, no primordial atmosphere, but a tenuous atmosphere from current outgassing.
Saturn's Tethys (530 km, 6.4x1020 kg, density 1.0), has been tectonically active recently. Tethys has an enormous trench some 65 km wide extending right across the surface, which may be an equatorial extensional rift.
Dione (560 km, 1.1x1021 kg, density 1.4), is spherical with longitudinal tectonic asymmetry, heavily cratered on the leading face, but less so on the dark trailing face, which seems to have been resurfaced. Dione has a global polygonal tensional fracture system, including the Latium rift valley, and also has been tectonically active recently. Fractures up to 600 km long radiate from some centers, as from Cassandra, Amata, and Turnus, which suggest diapiric uplift. (see map, p. 242-243 in Briggs and Taylor, 1982).
lapetus (730 km) is asymmetric in that it has a dark leading hemisphere and a bright trailing hemisphere, and has been volcanically ”resurfaced” so that no recent tectonic activity has been observed.
Similarly Rhea (765 km) has been largely resurfaced, but its Kuplum Chasma runs sharply northeast for 400 km. Charon, density only 1.4, and being solid, must be largely water-ice with little siliceous rock.
Charon's tectonic history is not yet known. Pluto-Charon density is 1.99 ± 0.09, very similar to that of Ganymede, Callisto, Titan, and Triton, indicating a combination of rock and ice.
Triton (564 km, density 2.06), is in a six-day retrograde, mainly circular, orbit only 3 million kilometers from Neptune, inclined at 160o to Neptune's orbit, precessing in 690 years. Its pole at present points toward Earth. The density matches the gas planets and their satellites rather than a rocky asteroid, so Triton may not be a captured asteroid, although such a capture event could account for the peculiarities of Uranus's orbit and obliquity, and Triton's retrograde orbit. Triton's composition - 70% rock and 30% water-ice-is a misfit in this region.
Power from the Sun averages only one W/m2, but Triton's internal heat source must be many times greater, as Voyager II found four active volcanic (or cryo-volcanic) sites, where plumes reached 8 km. Triton's mid-latitudes are criss-crossed by tensional fault scarps hundreds of kilometers long, which are lost under the wide polar cap of water-ice.
Uranus has four large satellites: Ariel and Umbriel, both 595 km in radius, Oberon, 773 km, and Titania, 805 km. Titania has several prominent rift valleys (Messina-1500 km, M. Jessica, Belmont, M. Bond) 50-60 km wide, and depths up to 6 km, which dominate the topography, along with many tensional fault scarps. Some of these rifts are the youngest features on Titania, cutting all else.
Oberon also has rift valleys, several hundred kilometers long and 74-80 km wide and 1-3 km deep, running latitudinally rather than longitudinally, and there are many smaller rift valleys and tensional fault scarps. The rifts vary in age, some pocked by craters, others freshened cutting across craters, suggesting that the extension is an ongoing process.
Umbriel is a dark satellite with only 0.21 geometric albedo. There are many prominent rift valleys and tensional fault scarps, which tend to spiral obliquely in latitude and longitude. Horst and graben patterns are common. The rift valleys are up to 60 km wide and as much as 4 km deep.
Ariel is dominated by rift valleys, mesas, tensional fault scarps, and later global rifting, which segmented the surface into quadrate blocks, somewhat like what happened on Miranda.
Radius >1,000 km and mass now ~1022 kg
This is the pre-lunar threshold. Geoidal shape is universal. Internal melting and volcanism are apparent. Polygonal surface rifting occurs in adjustment to waxing volume; outgassing continues with even a thin atmosphere.
Pluto, 1150 km radius, half that of Mercury, and mass 1022 kg, 1/400 of the mass of the Earth and less than one- sixth of the mass of the Moon. Pluto's volume is estimated to be 5.7 times that of Charon. Pluto's orbit is highly inclined (17o to the ecliptic) with large ellipticity 0.249), and relatively high density for that region (2.1 g/cm3) which have led several to suggest that Pluto may be an escaped asteroid.
The density indicates that Pluto contains about 75% siliceous rock and about 25% water ice and some methane ice. Pluto's orbit is very eccentric (4.5 AU at perihelion to 7.4 AU at aphelion. Resolution has not yet been good enough to see any tectonic features.
Europa (radius 1,571 km, mass 5x1024kg, density 3.04) is one of Jupiter's Galilean satellites. The surface is intensely fractured in a polygonal system of late and probably current tensional faulting; Europa has been resurfaced over all original craters. Individual dark bands 20-40 km wide are up to thousands of kilometers long. The most prominent system is equatorial, tipped 40o south toward Asterius Linea on 0o longitude, crossing the equator on 270o longitude, and continuous with Minos Linea 40o north on 180o longitude. The pattern is also asymmetric, with the fracturing much more intense in the hemisphere between 90o and 270o than in the opposite hemisphere (see the figure prepared from Voyager I and II in Briggs and Taylor 1982, p. 200-201).
Neptune's satellite Triton ( 1750 km radius) has a global net-like pattern of tensional lineaments tens of kilometers wide and hundreds of kilometers long, which cut across several areas of so-called ”cantaloupe terrain” - non-circular ringed mounds some 30 km in diameter, which Schenk ( 1993) has interpreted (from stereoscopic photo pairs) as gravity-driven diapirs, very similar to known fields of salt domes on the Earth, particularly those of the Iranian Great Kavir desert.
The differential relief is several hundred meters. Schenk suggests that the Triton swells are composite diapirs, consisting of at least two salts that have risen through a third ice. A layered crust less than 100 km thick consisting of ices (such as H2O, NH3, 2H20, CO2) is suggested.
Mass 1023 kg
A mass of 1023 kg is a significant threshold. All bodies are already spherical. Major volcanism on a grand scale indicates a differentiated interior. There is evidence of a magnetic field, which, on current theory, implies a fluid interior. Surfaces are riven by polygonal extension fractures.
Europa (radius 1563 km, mass 4.87 x 1022kg, density 3.0) a Galilean satellite has a circular 3.55 day orbit around Jupiter with zero inclination. The 0.58 albedo is larger than that of any of the planets or their satellites, so it is ten times as bright as Moon. The surface is intensely cracked with an expansion pattern.
Moon (1738 km radius, 0.749x1023 kg, density 3.34) has suffered intense volcanic activity in the past, though not active at present. The Moon is depleted in iron and in all elements more volatile than iron, particularly sodium, potassium, and rubidium, also waiter and sulfur Titanium is in excess, also refractory trace elements, such as barium, uranium, and the rare earths. Moon samples show remnant magnetism.
lo (1816 km, 0.89x1023 kg, density 3.1), slightly larger than Earth's Moon, is the innermost of the four Galilean satellites of Jupiter. Io has a very tenuous atmosphere, mainly oxygen, and an upper atmosphere of ions and electrons which yields brilliant aurorae, which imply a magnetic field. Io is very active volcanically, but it may be that we are witnessing Io at the time of a peak of activity. Io's volcanoes have developed a plasma torus of ionized gas around Jupiter. Io must generate a current of ten million amperes as it moves though Jupiter's magnetic field. Ice has been detected on Io by a satellite above most of the Earth's atmosphere.
(radius 2410 km, mass 1.06x1023kg, density 1.81 ) one of Jupiter's
Galilean satellites, has a crater coverage greater than any other body
in the solar system. The low density implies ices rather than silicates,
assumed to be water ice. But is this valid, or an earthling meme? Why not
ice of CO2 or methane? Callisto has no atmosphere, and no sign
of tectonism, which is exceptional.
Ganymede (2640 km, 1.5x1023 kg, density 1.93), is the largest satellite in the solar system. The low density indicates a great thickness of ices, perhaps an intergrowth of water ice and ammonium hydrate. The surface has many long mountain ridges, up to 7 km high and 10-15 km across, which must be supported by less dense material, because such departures from isostasy would have been corrected in time geologically short. There are polygonal dark and light regions from global expansion and many straight parallel ranges and valleys 10-15 km wide as high as the Himalayas. In some places there is clear evidence that the crust has been sheared with lateral displacements of at least 100 km, and localized crustal spreading extension.
Mercury 2 439 km radius, mass 3.3x1023kg, density 5.42, the densest (as decompressed) in the solar system. Mercury shows a global polygonal extensional fracture system which cuts across the craters, which is discussed in the next section. Superficially, Mercury resembles the Moon, but internally Mercury is more like the Earth.
Moon's density is 3.3, Earth's decompressed density is 4.4, Mercury's is 5.3, so Mercury must have proportionally a larger iron core than the Earth, almost as big as the planet itself, far more than the differential condensation model predicts. Some theorists have suggested that Mercury originally was much larger with a thick silicate mantle, which was boiled off early by a temporary solar nova-like blast, or by impact with a large asteroid.
Titan, 2575 km radius, 1.35x1023 kg mass, density only 1.9, Saturn's large satellite, nearly half as big again as the Earth's Moon, but it is less massive. Titan has 2o orbital inclination to Saturn's orbit, with a small eccentricity of 0.029.
Titan has a dense atmosphere reminiscent of Venus; the clouds at 30-40 km above the surface, which screens a frigid landscape. The nitrogen atmosphere contains 2% methane, and the surface may have lakes or seas of liquid ethane and methane in basins between hills of solid ammonia and methane ice, with an interior of water ice (see Figure 27 of Reichstein, 1985). Radar reflections (near the limit of resolution) reveal that one radar-bright region consistently appears 15 hours earlier than expected, indicating that the rotation period is in error by 49 minutes.
6.4x1023 kg 3 381 km radius density 3.94, has great shield volcanoes,
and great equatorial rift, and many regional tensional rift chasms. Photo
interpretation of Mars' surface indicates former winding river channels,
evidence of glaciers, stupendous floods, and perhaps an Ocean Borealis
(but, see page. 151.), with a former much thicker atmosphere protected
by greenhouse gases, fed by the great volcanoes (Figures 114 and 115).
McGill and Hills ( 1992) have described fields of gross polygonal cracking
on Mars, which recall the polygonal fractures on Mercury. The polygons
are 5 to 20 km across, bounded by grabens 200-800 m wide. Attempts to explain
them as desiccation shrinkage in 600 m thick sediment fail for several
reasons. As on Mercury they must be caused by global extension.
Density exceeds 5, a significant atmosphere is retained, there is a fluid core, extensive vulcanism, widespread tensional fracturing, a dynamo magnetic field, a magnetosphere, and the body is a net radiator of energy.
Venus, radius 6,053 km, mass 4.88x 1024 kg, density 5.26, orbital inclination 3.4o, eccentricity 0.0068, rotation period 243 days (retrograde). The adopted prime meridian is through the central peak of the Ariadne crater (44oN). Venus is our neighbour and cited as Earth's twin planet, but after mass, radius, density, and solar distance, the sibling status seems to end.
Venus differs markedly in the lack of a moon, unimodal surface altitudes, slow retrograde rotation, no magnetic field, surface temperature, thick optically opaque sulphurous atmosphere, virtual absence of free oxygen, high albedo, no geosynclines, no granites, no pyroclastics, no surface water, and hence absence of the water emission that dominates the Earth's land forms.
Very little was known about Venus' geology until the complete radar coverage by the Venus-orbiting Magellan satellite. A 628-page summary of the radar interpretation was published in August 1992 as volume 97, number E8, of the Journal of Geophysical Research.
It is unfortunate that this interpretation has been done by teams, who all believe in the plate tectonic model of an Earth of constant radius and compressional tectonics. Rather than the present Earth, the surface of Venus should have been compared with a Permian Earth (minus the hydrosphere and water- laid sediment) before the beginning of dispersion of the continental blocks, when the Earth was in about the, same expansion stage as Venus is today (that is when Earth was already 90% of its present age). The American interpreters could not miss the universal tensional faulting nor the universal diapirism, but their creed blinded them to the fact that this meant that Venus' tectonics are identical to Earth's
On Earth then, and on Venus now, there is no sign yet of continental blocks separated by mantle-derived” oceanic” basalts. The interpreters firmly believed that the main stress on Venus would be compression, and although they were always biased that way, none was definitely found, beyond diapiric spreading.
Venus' surface is unimodal, compared with the Earth's hypsometric curve, which is bimodal, corresponding to continents and oceans. Venus today resembles an early Mesozoic Earth of 300? million years ago, 10% behind Earth tectonically, before there were any great oceans on Earth. Mars is 50% behind Earth tectonically, Mercury 80% behind, and the Moon 95% behind - a sequence caused by size.
The blindfold of creed could be more serious. Instead of confining landforms to an Earth-model, surely we should be alert for basic differences from Earth. For example, what are the tesserae? They appear to be the oldest surface on Venus, and have been interpreted as intensely compressed folded strata-perhaps schists or gneisses. Is this valid? Having no water, Venus should have had no such strata! I address this question later.
Only 8% of Venus can be regarded as true highlands, with a maximum altitude 10 km above the plains. This recalls continental Africa. The lowest point on Venus is in a rift 2.9 km below the plains.
The most obvious features of the Venusian crust is the ubiquitous tensional faulting, on all scales from immense rift chasms to the limit of resolution of the pixels. Much of the surface resembles the surface of a glacier riven by millions of crevasses.
Major crustal spreading and diapiric rise of ”mantle” magmas on a large scale is widely acknowledged (Head and Crumpler, 1990). No subduction is reported, but it is assumed that it must exist, and has been buried by volcanic products which cover the plains. Imagined” plates” are also assumed to be somewhat ductile, rather than rigid as on the Earth. The next most conspicuous feature of Venus is the widespread volcanism, which covers 80% of the surface, the rest being” tessera”.
Earth (5.98x1024 kg) density 5.52. Earth is discussed in the next chapter. Consistent with its position in the size gradient, the Earth shows major expansion, double maxima in statistical altitude, major volcanism, an atmosphere, a magnetic field, and an ionosphere. The standard model has a thin silicate lithosphere, an iron-magnesium silicate mantle down to half the radius, then a liquid core of molten iron, and a small solid iron inner core. However, comparison between the equation of state of iron and empirical seismic data indicates that the core is ten percent less dense than pure iron at core temperatures and pressures, which implies a substantial amount of light elements. These could be silicon, magnesium and oxygen, the source of the mantle differentiates, but possibly also carbon, sulphur and hydrogen, which eventually reach the lithosphere (Yingwei Fei, 1995). Not indicated by the density deficiency but suggested by comparison with meteorites, the core iron is probably rich in nickel and chromium.
Above 6,000 km radius, and 1024 kg mass, expansion becomes increasingly rapid, with intense tensional rifts, even progressing to the separating of the lithospheric blocks. Such developed on the Earth in the Late Permian, and intensified during Cretaceous to produce bimodal surface altitude Compare Venus (6053 km radius), and the Earth (6378 km radius).
Mass 1025 kg
In my model, a major threshold is reached. Accelerating expansion overtakes cohesion, resulting explosive disruption. (Recall the behaviour cepheids, or the explosion of a proto-Sun to an Antares condition.) If the mass exceeds 1026 kg, gravitation is sufficient for the body to come together again, but at lower density, in the range 0.8-2 g/cm3.
Less than this, the body disintegrates-hence fate of Aztex to spawn the asteroids. Sun, Jupiter Saturn, Neptune, and Uranus have already disintegrated and come together again. If the expansion rate of the Earth since the Paleozoic is maintain the Earth will follow within 200 million years.
Uranus (25,900 km, 8.7x1025 kg). The rotating axis of the planet is inclined 88o to the ecliptic, that the south pole now points approximately toward the Sun. Uranus has nine narrow dark rings and nine tiny satellites within the Roche limit, and five similar satellites (Miranda 4.96 rU, Ariel 7.29, Umbrial 10.15, Titania 16.65, and Oberon (773 km, 22.27 rU), prograde and coplanar with the equator of the plane (except perhaps Miranda whose orbit is inclined 4.22o).
Neither Uranus' obliquity, shared by his satellite family, nor the offset of the magnetic field to this plane have been explained. An early major implosion before the formation of the satellites, has been suggested.
Neptune, mass 10x1025 kg density 1.66, albedo 0.4, ambient temperature 45oK, its axis inclined 47o to its magnetic field and 29o to its orbit, has Pluto in stable capture resonance (Figure 124). Neptune is a net radiator at 1014 watts at the top of the atmosphere.
Mass 1026 kg
Saturn, mass 5.68x1026 kg, density 0.69, inclination 26.44o, "surface” temperature 95oK, albedo 0.61, magnetic field 550 times Earth's field, has major rings and 23 known satellites. Saturn is a net radiator.
Mass 1027 kg
Jupiter (31,398 km radius, mass 1.9x1027 kg, (70% the mass of all planets), density 1.33) is already a brown dwarf, radiating at 1.8x1018 watts (nearly twice what it receives from Sun) in the infrared and long wavelengths. It has an intense magnetic field and magnetosphere, thick atmosphere, many satellites and rings orbiting within the Roche limit. McNally regarded the five [four] large ”gas planets” as ”failed stars”. Rather I regard them as embryo stars. The standard model for Jupiter has the outer one-fifth of the diameter of molecular hydrogen and helium increasing from a temperature of 165K to a transition at I0,000 K and 200 Gpa pressure to the main zone of metallic hydrogen and helium, which may continue down to a small rock core at 5000 Gpa and 25,000K. Water ice has not been found spectroscopically (Thomas S. Duffy, 1995), and its existence may be an Earthling meme.
Mass 1028 kg
The stellar threshold is reached, the minimum mass to sustain nuclear fusion. The body is now a red dwarf on the Hertzsprung-Russell main sequence, proceeding thence through yellow and white stars to blue stars of mass 1040 kg, and so on to supernova explosion.
Mass 1029 kg
The threshold of a true star, for example a-Centauri B - a small hot star, with strong spectral lines of Fe2 and Si2 but not of hydrogen, the binary companion 300 AU from a-Centauri.
Rising internal temperature reduces density through both thermal expansion and mineral paramorphism such as the eclogite-gabbro transformation. Because of feedback, convective ascent becomes increasingly localised to form surface tumours, and asymmetry of figure, such as the distribution of volcanism on Mars (Figure 114) and the Earth's Jurassic basalt volcanism.
As departures from isostasy relax in times geologically short, diapiric tumours, while standing higher isostatically, contribute greater moment of inertia, which perturbs rotation. The rotation axis then creeps toward the axis of maximum moment of inertia. Expansion is expressed through the solar system by asymmetric tumours, distortion of figure, and by obliquity to the ecliptic.
Geologists, geophysicists, and astronomers believe that the Earth's obliquity to the ecliptic is about 23o, has always been 23o and will always be 23o, notwithstanding large polar wander over the lithosphere. On the contrary, I suggest that the obliquity itself is a most important variable of paleogeography.
Whenever asymmetric volcanism, orogenesis, or glaciation causes a tumor on the spheroid, isostasy quite rapidly redistributes the load gravitywise, but leaves the moment of inertia greater at the tumour, which results in internal creep until the Earth rotates about the axis of maximum moment of inertia.
During the late Devonian and early Carboniferous, I suggest that Earth's axis was roughly normal to the ecliptic, the humid tropics spread 60o north and south of the equator, sunlight was tangential at both poles even in winter, and the Lepidoclendron flora ranged throughout.
During the later Carboniferous and Permian, obliquity was large, with long polar winters, glaciation was widespread, and the humid tropics were narrow, separating a Glossopteris flora in the southern hemisphere from a Gigantopteris flora in the northern hemisphere. By the Jurassic, the obliquity was small again, the humid tropics wide, and the cycad floras spread throughout.
of Earth, Moon, Mars, Venus, Mercury, Jupiter, Saturn - all record their
asymmetric expansion in their obliquity to the ecliptic:
Likewise, the excess development of new ocean floor in the Pacific, biased as it was in longitude, and even more biased in latitude, would have reached isostatic equilibrium relatively rapidly, but this would have upset the balance of the moment of inertia, because oceanic crust in isostatic equilibrium stands several km lower than continental crust.
The most obvious and striking feature of Venus is the ubiquitous myriads of tensional faults, grabens, and chasms. Younger rifting on Venus is biased very strongly to one hemisphere. Schaber et al. (1992) show that in one hemisphere younger impact craters are severely modified by concentrated extension, while the opposite hemisphere has pristine impact craters that seem unaffected by tectonic, volcanic, or other processes, although the frequency of craters is statistically similar in both hemispheres.
Both volcanism and tensional fracturing on Venus are almost universal, But both show hemispheric asymmetry. Although cratering is randomly distributed, the craters are strongly modified by tensional faulting in one quadrant. Head et al. report:
Mars likewise records asymmetric diapiric expansion. All the volcanoes of Mars are in one hemisphere, indicating asymmetric diapiric expansion (Figure 114). The great glaciation of the southern hemisphere (described in detail by Baker and his five co-authors, 1991 ), and the great Oceanus Borealis (Figure 115) emphasize this asymmetry, and so does the great equatorial rift valley Valles Marinensis (Figure 114), which repeats the Archean condition of the Earth.
The asymmetry of Mars is conspicuous. Not only do all known shield volcanoes occur in one hemisphere, along with the great Tharsis bulge of the Martian figure and also the Elisium bulge, but the Boreal Ocean is most extensive in this hemisphere.
The Austral Ice Sheet is mainly a southern-latitude phenomenon, extending at maximum even to the equator along the Tharsis-Elysium depression, while the complementary Boreal ice cap only extends l0o from the pole. This may be due to the precession of the rotation axis, which is large on Mars because of the asymmetry of figure.
Schultz (1989) follows the false meme that the "wrinkle ridges" are compressional, whereas they are part of the global extensional pattern of Mars. I agree with Schultz in identifying strike-slip faulting on Mars, but he is in error in assuming the minimum stress S3 to be vertical, whereas strike-slip faulting implies that both S1 and S3 are in the strike plane of the fault.
For this discussion assume arbitrarily that the rectangle of his Figure 3 is oriented with the top and bottom east-west and the sides north-south, then in his Figure 3a. the illumination is from the NNE, the sinistral slip-fault trends east-west, tensional faults and grabens trend NW-SE, and compressional folds and faults would trend NE-SW. This is exactly what occurs. The rims of the wrinkle-ridges and the rims of the tensional grabens associated with the strike-slip faults trend NS-SE, as do their shadows. There are no compressional structures.
Like Earth and Moon, the figure of Mars is “pear-shaped”, but on Earth the hemispheric differences are only tens of meters, whereas on Mars the southern hemisphere is 2 km above the rotational ellipsoid. As gravity rules in times geologically short, this means that less dense rock persists to great depth in the south.
Jupiter's Great Red Spot, 46,000 km long, has been stable for at least three centuries, and it may be anchored over some special asymmetry on the” rocky surface” but no evidence suggests that Jupiter has a solid surface, except perhaps a rocky core less than 15% of Jupiter's radius.
The alternative, that the spot is a stable vortex in an entirely fluid system has had some success in computer simulations (Ingersoll,1988). The spot rolls like a ballbearing between an eastward flow on the north and a westward flow on the south at differential velocities of hundreds of km per second. The flow in the spot is convergent and downward - an anti-cyclone.
Ostro and his co-workers (1992), in 13 cm radar, observations from Arecibo, report a weak hemispheric asymmetry on Jupiter's satellite, Callisto. Saturn's satellite Iapetus has a pronounced albedo difference between the dark leading hemisphere and the brighter trailing hemisphere. Several others are similar, and there is debate as to the cause.
Moon has a bulge facing the Earth. All the great volcanic maria (Imbrium, Serenetatis, Tranquilitatis, Nubium, Humorum, Fecunditalia, Crisium), which ascended diapirically when molten, are in this hemisphere, so that this hemisphere stands higher when in isostatic equilibrium. This bulge faces the Earth, just as the long axes of Phobos and Deimos always point toward Mars.
The gravity attraction of the Earth raises reciprocal tidal bulges above this isostatic equilibrium figure. As the Moon always presents the same face to the Earth, these tidal bulges are virtually fixed.
Mercury has a global polygonal system of fractures, hundreds of kilometers long with scarps up to 3 km high (but usually less), which cut across most craters (except late ones). Strom, when he first saw them after the first Mariner-Ten Mercury flyby, suggested that these” lobate scarps” might be compressional, perhaps the result of the congealing of the liquid interior, resulting in a 1 % global shrinkage, and this interpretation has progressively been adopted as fact.
Briggs and Taylor (l982), still with the compressional assumption, suggest that they may be due to stresses caused by the de-spinning of Mercury's rotation to its 3:2 resonance with the Sun. But this should have occurred long ago, whereas the polygonal fracture system is recent, later than most of the craters. Although all craters must be underlain by brecciated, fused or shattered rock, the lobate scarps ignore the existence of craters, which suggests a deep cause, as does their pan-global distribution.
The lobes are markedly asymmetric, and tend to be concave toward the lower side and rounded on the upper side, falling gently away. I suggest that they may be really tensional, due to the secular and increasing expansion of the planet. I see no morphological difference between them and the lobate scarp rings that encircle Caloris and are accepted without dispute as tensional. In several places intermediate levels step down in a pattern typical of tension faults, but with no sign of compressional overriding.
At no point do they show any foreshortening of the craters they intersect. Where the fractures cut a crater, the rim may be shifted back, increasing the area of the floor, not foreshortening it. In some places there is a rift valley between two such faults of the system (as Arecibo vallis near 28oS 22oW).
Near this locality, as in many other places, two through-going faults of this system meet nearly orthogonally, which is characteristic of epeirogenic fault systems, but not of compressional systems. Another example is on the resurfaced plain east of Caloris, where a NE-SW lobate fault converges on the rim of an old resurfaced crater to terminate on an E-W fault, cutting across the old resurfaced floor (with several anastomosing rift valleys).
There is no foreshortening of the old resurfaced crater rim, and right at the junction of the two faults there is the palimpsest of an old crater with a circular rim and no sign of foreshortening (Figure 9 of Strom et al., 1985). In their Figures 15 and 16 they cite a 65 km crater where the rim appears to be offset about 10 km by one of the lobate faults.
But in this case the crater rim is completely lost in a black triangular shadow, and whereas the edges of the shadows are offset, the actual rim offset is probably zero. Even if an inward dip of the convexity be confirmed, an uplifted block of this magnitude (given Mercury's high surface g), would spread to overhang its borders.
The global expansion pattern is consistent with the probability of a fluid interior indicated by Mercury's magnetic field, and also brings Mercury into harmony with the sequence of Moon, Mercury, Mars, Venus, Earth with progressive expansion related to mass.
Volcanism or cryo-volcanism starts to appear at mass 1019 kg, and is general at 1020 kg. NASA analysts frequently refer to” resurfacing” of planets and their satellites, where they lack established cratering episodes, which have therefore been presumed to have been obliterated by burial during global volcanic (or other) processes. For example, on Venus events prior to the inferred Cambrian are totally missing, replaced by extensive plains. Each such resurfacing event implies a blanket a few kilometers thick, which suggests that the mean radius of the planet has increased by this amount.
On Mercury extensive smooth plains have been interpreted as volcanic flows perhaps similar to the Moon's maria, but others consider them to be ejectamenta blankets. No specific volcanic morphologies, other than the resurfaced plains, have so far been identified on Mercury. The late global polygonal fracture pattern, the emission of radio waves, and the magnetic field may indicate that the planet's interior is now hot and currently heating up, in line with the model of continuing growth.
On Venus, volcanism has been very active throughout time, which has produced the Venusian atmosphere. Ubiquitous vulcanism, covers 80% of the surface, the rest being” tessera” , which may also be earlier volcanic material. Head et al. ( 1992) report 550 volcanic-shield fields, 274 intermediate-size volcanoes, 156 volcanoes more than 100 km in diameter, 86 crater-centered volcanoes, 175 ”coronae”, 259 ”arachnoids” , 50 ”novae” , 53 lava fields, and 50 sinuous lava channels, but no evidence of pyroclastics.
There are great shield volcanoes, hundreds of kilometres across, which likewise must be near isostatic equilibrium. Thousands of smaller volcanoes, still large by Earth standards, which have oozed forth great lava floods, repeatedly resurfacing the ;expanding planet. More rarely there are more viscous lavas. Most magmas seem to be basaltic, but some of the lavas flow in kilometer-wide channels for Several thousand kilometers. What sort of magma is this? No Earth-known magma could do this. Could the surface temperature and pressure (>300oC and >90 bar) sufficiently inhibit the loss of fluidizing gases?
The distribution of volcanism is universal, not on linear plate boundaries. The broad lowland flow plains are deficient in volcanoes (like the cold thick crust within the second order tensional polygons on the Earth). ”Coronae” , mound-like tumors, hundreds of kilometers in diameter, which on that scale could not survive long unless near isostatic equilibrium, with the weight of a less-dense rock column below balancing the general weight of either columns.
It is doubtful whether there was ever any oceanic water on Venus in the past before its evaporation by greenhouse heating, because nothing resembling sediments has been found.
Volcanism has always been prominent on the Earth, from early komatites, vast basaltic floods and shield volcanoes, through granite batholiths with large volumes of pyroclastics, to the vast basaltic ocean floors making up half of the total surface of the globe, which date only from the last twentieth of geologic time, due to the Earth's accelerating expansion.
The Moon does not appear to be currently active but has experienced extensive volcanism in the past, indicating a molten interior then. Don L. Anderson (from attenuation of S waves, electrical conductivity, high heat flow, and surface concentration of U and Th) has suggested that the Moon may still have a molten core, but not of iron.
Lunar rocks and soils are depleted in volatile elements, much more so than on the Earth. Iron is 25% of expected cosmic abundance, and elements more volatile than iron are depleted. Oxygen isotope ratios are similar to the Earth.
Mars has evidence of former extensive volcanism, which caused” resurfacing” of broad areas of the planet, and of relatively recently raised enormous shield volcanoes, which are confined to one hemisphere (Figure 114).
Jupiter being gaseous at least to great depth has no volcanism of his own, but there was repeated volcanism on all his satellites, except the smallest. Even Europa, only 781 km in radius, was volcanically resurfaced not long ago, because there are few craters. Ganymede shows past volcanic resurfacing, and tectonism has been strong in the past. Although no volcanic activity is observed at present, all early cratering has been completely resurfaced by recent flows.
Io is currently the most active in the solar system with a brilliant red surface and eight or more volcanoes, hurling clouds of sulfur and SO2 100 km or more above the surface; there are craters filled with molten” lava” which has extruded for considerable distances.
Current opinion regards these lavas as molten sulfur. But Io is denser than Moon, so rocks are indicated below the surface. Io's volcanoes have generated a plasma torus of ionized gas around Jupiter. But at Io's size, even with normal radio- activity, it should have frozen solid long ago, so whence the heat?
Of Saturn's satellites, Mimas, being just below the critical threshold, lacks volcanic resurfacing or tectonism. Iapetus has been volcanically resurfaced with the result that no recent tectonic activity has been observed. It is volcanically asymmetric in that it has a dark leading hemisphere and a bright trailing hemisphere.
Likewise on Enceladus any tectonic record has been covered through volcanic resurfacing, although a body the size of Enceladus (only 251 km radius) should have frozen solid quite early, so such volcanism should not have occurred. Rhea has been volcanically resurfaced, so no recent tectonic activity is observed.
On the satellites of Uranus, Umbriel seems to have been resurfaced by early volcanism, and there is evidence of more localized vulcanism. Miranda (242 km in radius) should be dead and lifeless, whereas it has certainly been tectonically and volcanically active very recently. Miranda's internal heat source is still a problem, being too far from Sun to have a molten core and too small to keep one - except perhaps through cold fusion!
Titania's smooth plains are believed to be cryovolcanic flows. Some lineaments of small craters may be endogenic cryovolcanoes. Ariel was resurfaced, covering the early intense cratering (but leaving some large crater palimpsests), followed by more cratering without any large craters, and then later followed by the global rifting. On Triton, Voyager II found four currently active cryovolcanic sites, where plumes rose 8 km.
This review shows that volcanism has been universal throughout the solar system in all bodies, planets and satellites alike, above 200 km in radius, irrespective whether they are in the inner or outer part of the system. (Ceres is in this range, but no probe has yet been near enough to determine her volcanic status.) Whence this heat? Primal heat is quite inadequate, so is gravitational energy from compaction and consolidation.
Astrophysicists have adopted the meme as unquestioned fact that evolution since the initial proto-Sun nebula has been cooling down, without any new source of heat. Consolidating bodies have gained heat locally to reach initial melting, and some heat has been released at a logarithmically diminishing rate by radioactive decay. Astronomers have sought to explain heat anomalies by rotation spin-down, and by tidal friction, but when such sources are exhausted, bodies cool toward absolute zero. The anomalies remain.
However, as explained in the next chapter on stars, cold fusion should proceed at vanishingly small rates even in small bodies, increasing logarithmically with waxing temperature and pressure in the cores of larger bodies. So all bodies in the solar system progressively increase in mass and volume at rates depending on their mass.
As the Earth doubled its surface area since the Paleozoic without significant change in surface gravity, its mass must have increased by a factor of about 4 in the last 300 million years. So must have Venus, Earth's twin, where as Jupiter would be much more advanced, and smaller planets and satellites well behind in this logarithmic progression.
Magnetospheres are a normal feature of rotating planets and stars, and even galaxies. Venus, so similar to the Earth in many respects, has virtually no rotation and no detected magnetic field. The Earth, with constant rotation, reverses the polarity of its field every few million years, and the magnetic axes of Uranus and Neptune are at large angles from their rotation axes, so rotation per se cannot be the sole determinant.
Substantial unexpected differences between the planetary magnetic fields implies that our conceptual models of planetary fields are not yet satisfactory. Magnetic forces are orders of magnitude greater than gravity. Gravity is constant, and acts in the line radially outward from every body. Electric and magnetic forces are in the plane normal to gravity, and normal to each other. Opportunity here for an original mind!
Irrespective of rotation, bodies less than 3x1023 kg, that is smaller than Mercury, do not have detected magnetic fields. Some Moon rocks have remnant magnetism, indicating a magnetic field, at least in the past. This should not be, but cold fusion could explain it. Io, only slightly larger than the Moon, displays brilliant aurorae, implying a magnetic field.
Mercury has a small dipolar magnetic field, perpendicular to the ecliptic and about 1 % of the strength of Earth's field, which produces a small Earth-like magnetosphere, but no ionosphere. An active dynamo circulation is hypothesised to produce Mercury's observed magnetic field, which is difficult to explain unless there is an additional unexpected source of heat; otherwise the core should have congealed long ago, unless there is heat from slow cold fusion as suggested previously. However, Mercury's rotation rate is too slow to fit the dynamo model.
Mars may have an intrinsic magnetic field as reported by the Russian probe Mars V, but it must be very weak and has not been confirmed. Mars does have a magnetic tail however produced by detection of the solar wind by the ionosphere (Saunders, l989).
Venus's very slow rotation may be the reason for its lack of a magnetic field. This supports the current magneto-hydrodynamic model for planetary fields.
The Earth's strong field of nearly one gauss is interpreted as produced by magneto-hydrodynamic circulation of the electrically conducting fluid core, which produces a strong toroidal field and the observed secondary geomagnetic field. Paleomagnetic studies prove the existence of this field at least for 2x109 years, probably longer.
The repeated polarity reversals of the Earth's field, and long periods of magnetic quiet have not been explained. Gross” wander” of the magnetic poles may be due to thermal geotumors and to asymmetric relative motions of continents whose centers of gravity are higher than equivalent oceanic sectors, both of which disturb the moment of inertia. Rotation poles continually migrate so that the body rotates about its maximum moment of inertia.
Some meteorites have remnant magnetism. Is this a palimpsest inherited from the postulated Aztex planet?
Jupiter's magnetic field of more than 10,000 gauss, inclined 9.6o to the rotation axis (which is tilted 3.1o to the ecliptic), is much stronger and more complex than any other in the solar system. The Earth's magnetosphere is shaped like a teardrop, but Jupiter's is much flatter, stretching away from the Sun in the ecliptic plane some 1000 times Jupiter's radius, and about 100 radii forward toward Sun, but less than 50 radii normal to the ecliptic.”
The sulfur and oxygen plasma sheet originating from Io carries a billion ampere current, which generates its own magnetic field, supplementing Jupiter’s internal magnetic field. This term is the inner part of Jupiter's magnetosphere.
Saturn has a strong field, a little smaller than Jupiter's, but extending well beyond the rings. The magnetic axis coincides with the rotation axis - a problem for the dynamo theory which requires an angle between the magnetic and rotation axes - on Saturn both are inclined 29o to the ecliptic.
Uranus also has a magnetic field of about one gauss which has bizarre geometry, being a dipole offset some 380 km from the planet's center and tilted 57o to the axis of rotation (itself inclined 88o to the ecliptic), so that the magnetic poles lie in latitudes 33o North and South and the rotation axis points to the Sun. Miranda produces an aurora. The magnetic field implies a fluid interior.
Neptune's rotation axis is 29.6o to the ecliptic, but the magnetic field is tilted 47o in the opposite sense, and the axis of the magnetic field is displaced by over half the planet's radius from the planet's center. So the surface strength of Neptune's magnetic field varies greatly with longitude.
All this complicates Neptune's interaction with the solar wind. Neptune has a doughnut-shaped radiation zone similar to the Earth's Van-Allen belt, generally inside the orbit of Triton, Neptune's largest satellite. There is a strong aurora on the sunlit north pole, but the aurora on the dark south pole is relatively weak, emitting only ten million watts, compared with the Earth's equivalent 100 billion watts.
Neptune's magnetosphere extends some 870,000 km toward the Sun and more than 6 million km away from the Sun. There are no magnetic data yet from Pluto.
Clearly many anomalies in the magnetic fields of the solar system remain to be understood. We still have much to learn.
In general, the outer ”gaseous planets” , Jupiter, Saturn, Uranus, and Neptune have nearly primordial atmospheres, retaining them because of their remoteness from the Sun, and their high gravity. The inner planets, Mercury, Venus, Earth, and Mars, have widely different atmospheres because of net loss and lower gravity, which failed to prevent escape.
Atmospheres are not static. Early loss may be from initial high temperature, initial low mass, and impact depletion. The Earth's early CO2 was absorbed in carbonates, and late oxygen was entirely developed by photosynthesis.
are derived by outgassing from the interior by volcanic emissions.
The small satellites have no atmospheres, and the larger ones have only
minor atmospheres from current emissions. The residual gases are water,
carbon dioxide, and nitrogen.
Mercury has a very tenuous atmosphere of 02, Na, and H2 at a pressure of only 2x10-12 bar and also 2 spectral lines of Na and K, maintained by current outgassing, and perhaps partly produced by the impact of the solar wind and meteoroid flux. Mercury has been assumed to be the refactory planet, condensed from where the solar nebula was still dense and hot, so that non-volatiles (materials with high boiling points) survived, others migrated to condense farther out.
Hence Mercury's richness in iron and silicates its a sequence through Venus and Earth to volatile-rich Mars, carbonaceous and water-rich asteroids, to the icy and gaseous giants. Radar reflections indicate the presence of a little ice (or radar-similar substance) at Mercury's poles.
Mars has a thin carbon dioxide atmosphere at a pressure of 7x10-3 bar. Mars suffers global dust storms, which obliterate the highest mountains (like the Olympus Mons complex) so that Mars looks like Venus for several days.
A main Martian Amazonian-age glaciation has been described by Baker (1991) and his five coauthors from which the Kasei ice sheet discussed above would have been a maximum-extension stage (Figure 115). A few impact craters are later than this glaciation, and the main tensional rift region of Chiasma Marineris would have been filled with ice, but rifting continued after the glaciation, because many of the landslide features in the chasm are relatively young and not affected by glaciation.
Venus whose surface temperature is >400oC, has a dense 90-bar atmosphere of CO2 (96%), N2 (3.5%), H20 (50 ppm), SO2 (20 ppm), and particulate matter including elemental sulfur. The total amount of nitrogen is similar to the Earth's, but is diluted by the much higher proportion of CO2 on Venus. The mass of CO2 is also similar, but much of the Earth's CO2 has been precipitated out as limestone and dolomite. Only the Earth has life to generate oxygen. Earth's excess nitrogen remains a problem.
Droplets of H2S04 are abundant in the highest levels of the atmosphere. Venus contains higher concentrations of the inert gases other than radiogenic argon. Significantly less 40Ar occurs on Venus, which may mean less potassium in Venusian rocks. The deficiency of the heavy noble gases may mean that the Earth lost them during the early collision advocated by Ringwood to produce the Earth-Moon binary (see p.166). A marked feature of Venus is the deficiency of hydrogen as water or otherwise.
On Venus 75% of the heat radiation from the Sun is reflected back into space, because of the high albedo. Despite the great depth of the atmosphere, it proved to be unexpectedly transparent, with nearly 3% of the solar flux reaching the surface, but in completely scattered form. Wind velocities vary greatly with altitude and latitude: 100 m/s has been measured in the upper atmosphere, and equatorially at lower levels, but wind speeds are less than IO km/s at 10 km altitude, and near zero at the surface.
Hence wind erosion and dunes are minor, although more than three thousand wind streaks have been identified, predominantly in lowland regions as wind shadows of ridges or hills, more often wind-longitudinal (where wind can bottom the mobile sand to bare rock) or transverse (where the loose material is too thick). The mobile fragmental material seems to have an impact source, not tuff. There is global ”Hadley” type circulation on Venus, which tends to equalize temperatures between the tropics and poles.
The Earth has an atmosphere of Na (79%), O2 (20%), Ar ( 1 %), and traces of H2, H2O, CO2, and virtually none of the noble gases He, Kr, and Xe. Such an atmosphere is quite abnormal. The amount of N, is four times normal, and the virtual absence of the noble gases compared with solar and cosmic abundances, needs explanation.
It means that the primitive. atmosphere was entirely lost in Hadean times through high temperature planetary collision as advocated by Ringwood, or was swept away by the solar wind. The present secondary atmosphere came from subsequent volcanic outgassing, and perhaps partly from meteor or comet infall. The O2 has been released by biosynthesis, CO2 has been consumed by organisms and partly secreted as limestone and dolomite, the Ar is the radiogenic isotope and has accumulated through the decay of 40K.
be all atmosphere, conspicuously zoned into pink, brown, yellow, and white
belts, rotating at several hundred of kilometers per hour, with zonal differences
of 205 km or more, with many eddies. Aurorae and lightning are prominent.
Jupiter's atmosphere, said to be 8,500 km deep and half the planet's mass,
consists principally of hydrogen and helium in the solar proportion of
four to one. Infra-red spectroscopy indicates many trace gases:
Io has a tenuous atmosphere and an upper atmosphere of ions, and electrons yields brilliant aurorae. Ganymede appears to have no atmosphere because Voyager I recorded no dimming when the star k-Centauri was occluded by Ganymede, but some argue that Ganymede may still have a tenuous atmosphere of water vapor, or of oxygen from the sunlight disintegration of water vapor.
Saturn's atmosphere (assumed to be the whole planet) resembles Jupiter's, mainly hydrogen and helium, but methane, ammonia, acetylene, propane, and phosphine have been detected spectroscopically. Zonal banding is much less prominent than on Jupiter, and of course it is much colder, with clouds of ammonia ice. Equatorial wind velocities approach 2000 km/hour (four or five times faster than Jupiter's)
Titan has a thick atmosphere of nitrogen 15%, argon 15%, methane 2%, and traces of ethane, acetylene, ethylene, and HCN at a pressure of 1.6 bars, (density four times Earth's) which gives an optical whiteout like Venus. Only Titan and Earth are known to have atmospheres so high in nitrogen, and the source of the nitrogen is a problem for each. What does this mean? Titan's atmosphere has a bronze-orange haze presumably caused by cosmic rays and solar ultraviolet radiation exciting organic molecules. Lakes of liquid nitrogen and of methane may exist at the poles, along with methane ice. Conceivably a self replicating molecule and life, quite different from ours but consistent with the prevailing environment, could be contemplated. Enceladus has no atmosphere.
On Uranus the upper atmosphere is 90% H2 with less than 10% He, zonally banded like Jupiter and Saturn, with a pressure of 0.4 bar. As the mean density is only 1.18, the atmosphere must be deep, with ices making up much of the solid body. The exosphere is predominantly atomic hydrogen. The endogenetic heat flow of Uranus is 1014 joules/s (80 x 10-6 joules/Cm2) at the top of the atmosphere.
Andrew Ingersoll is reported to have described Neptune as having ”a Mach-one atmosphere” ripping to the west up to 600 m/s, with differential winds approaching the speed of sound.
Triton has a thin atmosphere of N2 with 1 % CH4, and traces of CO and CO2, which is in equilibrium with surface solid nitrogen, water ice, and methane ice. There is a polar cap, and possibly an ocean of liquid nitrogen. Recently, Dale Cruikshank has reported larger amounts of CO2.
Pluto has bright polar caps and a less reflective equatorial band, with two large spots, one bright and one dark. McKinnon and Mueller (1988) have estimated that Pluto has a surface layer of methane ice a few kilometers thick, then a shell of water ice between 200 and 300 km thick, overlying a core of partially hydrated rock. Occultation of a twelfth magnitude star by Pluto established that Pluto possesses a thin atmosphere. This consists of methane, with smaller amounts of N2, CO, and O2 at a pressure of 10-5 bar. Charon has a thin atmosphere of methane crystals with minor amounts of N2 CO, and O2.
Because water is such an abundant, ubiquitous, and life-essential substance on the Earth, our natural assumption is that this applies throughout the solar system.
According to Ringwood (1977), the majority of asteroids are similar in composition to type 1 carbonaceous chondrites, which contain up to 20% water, bound in hydrous magnesium silicates, so there is no shortage of water in the asteroid belt. Such carbonaceous chondrites, are thought to be primitive, and hence samples of the material from which the inner planets developed.
All Apollo samples from the Moon are completely dry, and unlike Mars, there is no evidence of former water. It is assumed that all water in the original accumulation of the Moon was used up oxidizing the iron, with the escape of the hydrogen so released.
Mercury is very similar to the Moon - no water at all, nor is there evidence of its former existence. Any water originally present would have oxidized iron, and the hydrogen would have escaped.
The total volume of water on Venus is very low compared with the Earth; There is no surface water and no sign of aqueous sedimentation, so the present high surface temperature of 500oC must have prevailed since early times, because although seas could have evaporated, ancient sediments should still be there. Early history of sedimentation on Venus may have been obliterated by volcanic” resurfacing” .
Thomas Donahue of the University of Michigan has argued for a former aqueous Venus with some 20 m of coverage of the whole planet. there is no evidence for this. Granitic batholiths could not exist because Venus has nothing comparable to a geo- syncline, and the temperature at the surface being above the critical temperature of water, would be progressively higher below. Hence neither granitization nor hydrothermal veins should exist. Nor should there be be tuffs or pyroclastics on Venus, because such are produced when temperature- pressure conditions drop below critical, and gas-phase water flashes explosively into steam.
What then are the tessera? Geologists familiar with air-photographs of intensely folded rocks on Earth immediately recognized the tessera on the radar-generated images of Venus as similar. Surely this implies a thick mass of sediments before the intense folding'? And after the intense folding a very long period of water erosion to bevel them off to a peneplain. The peneplain implies prolonged base- levelling to sea-level.
Where now is the vast accumulation of sediments from the base-levelling of the intensely folded rnountains? Where has the sea-water gone? It is not there now, nor in the atmosphere which contains only a Few parts per million of water!
Could the plateau surface of tessera be not a peneplain erosion surface but a geoid level determined by gravity? If so, tessera are not intensely folded and peneplaned strata! What then? Could they be relics of a flow surface dating from an early molten or plastic stage of the planet? Not very convincing, but neither is the interpretation of intense folding and peneplanation.
The Earth's original atmosphere was lost during the early molten stage, or during Ringwood's postulated gross collision from which the Moon emerged. The whole of the present atmosphere and hydrosphere has been produced through volcanic activity through geologic time. Little of this has been lost, so most of it is still here. Widespread Proterozoic dolomite and limestone locked up CO2 (the total proportion of CO2 in this form is comparable with the total CO2 in the Venusian atmosphere). During the last third of geologic time the oxygen was generated by the biosphere. Earth gravitation has been sufficient to prevent the escape of accumulating water which was present even in early Precambrian time to from primitive seas.
On Mars volcanism is prominent and would have produced water. The surface is too cold for the existence of liquid water. But not far below the surface, temperature conditions could have been right for the formation of hydrothermal veins. Mars has polar caps, originally thought to be CO2 ice, but now known to include some water ice with frozen CO2 but the present thin atmosphere of Mars is mainly CO2.
Williams and Zimbelman (1994) have interpreted a unique 15 km diameter mass of ”White Rock”, nearly 600 m thick, in an 80 km diameter crater by that name, as a residual sulfate deposit from the evaporation of some 200,000-130,000 km3 of Earth- seawater equivalent. They cite the gypsum deposit in Lake Lucero, New Mexico, as a possible analogue. The White Rock has through-going parallel kilometer-wide gashes, that do not extend regionally, which they state go down only to a depth of about 360 m. This would be a fairly normal depth for creep closure of tensional gashes. Large circumferential cracks which seem to be tensional, also cover the wider half of the body. Although I do not offer any convincing alternate explanation of this puzzling feature, I do not accept the evaporite interpretion.
Photo-interpretation of Mars' surface indicates former winding river channels, evidence of glaciers and massive floods and perhaps Oceanus Borealis, with a much thicker atmosphere protected by greenhouse gases fed by the great volcanoes.
Controversy has surrounded the origin of the great ”outflow channels” of Mars, interpreted by most as the result of colossal floods, greater than anything else in the solar system (Robinson and Tanaka, 1990), or by wind erosion, or by glaciers (Lucchitta, 1982; Kargel and Strom, l992).
The outflow channels start with full volume at a tensional rift or from a large crater, head in a wide channel filled with” chaotic” terrain, form deep striation-floored channels 100 km to more than 200 km wide, which may anastomose.
They round off projecting walls to a flow curve, and divide around teardrop islands rounded upstream with a long downstream ”tail” . They peter out as abruptly as they started, vanishing in a plains area, without conspicuous sedimentation.
Melosh and Vickery (1989) have suggested an early atmosphere of at least one bar was dissipated and eroded by the early heavy cratering. This would not solve the problem of great aqueous erosion, because the heavy bombardment was early in Martian history, whereas the evidence of vast floods on the present landscape was very late.
The catastrophic flood solution is modelled on the scablands of Washington State following the collapse of former Lake Missoula. But the discharge from the Kesei channel alone (109 m3 s-1) has been estimated at two orders of magnitude greater than the Missoula flood.
The problem remains the source and the discharge rate of so much water on a relatively arid planet. A glacial solution is more probable, implying that the hundred-kilometer-wide longitudinally-striated valley floor was not eroded out by a colossal flood but by slow-moving glacier ice.
The channel floor rises more than 500 m where the Kasei channel sweeps from a northerly course to easterly (see Fig.10.14 of Carr, 1981; or Fig.4 of Robinson and Tanaka, 1980), and the drumlinoid lineations flowed smoothly over this at an earlier stage when the ice was thick, but became heavily crevassed for 30 km over the ridge when later the ice became thinner, so that at the base the crevasses in the residual ice cap on the ridge fed esker streams which flowed for 100 km over the earlier striated floor, ending in a braided pattern.
But is this
reputed glaciation of Mars valid? The present Martian atmosphere is:
Are there alternative
erosive agents other than water ice which could produce similar topography?
Given Mars' carbon dioxide atmosphere, a porous regolith should be saturated
with CO2, which with prevailing temperatures would become C02
ice. A regional volcanic event could extrude vast volumes of gaseous CO2,
roaring out from fissures, breaking the surface to chaotic terrain, but
immediately freezing to CO2 ice on meeting the cold atmosphere,
and flowing away as a CO2 glacier!
Salt glaciers flow for kilometers in Persia. Could CO2 glaciers flow on Mars, in due course to sublime into thin air, leaving no sediment deposits, as the Martian” glaciers” seem to do? At least we know the carbon dioxide is there, whereas the water is hypothetical, an earthling meme.
All the large planets - Jupiter, Saturn, Uranus, and Neptune - have many satellites, and multiple rings. All the rings are inside the Roche radius and are probably disintegrated satellites. Edouard Roche showed in 1849 that a liquid satellite of a planet or star could not form or survive closer than 2.44 times the radius of the primary of the same density.
At this distance a satellite's internal gravity equals the gravity attraction of the planet, and, without cohesion, the satellite would disintegrate. The larger the'' body, the less its cohesion can hold it together. This was suggested more than a century ago by Edouard Roche himself, but at that time he did not suspect that the masses of the primaries were growing with time, as I now suggest.
The alternate view is that during the generation of the planetary satellites, none could survive within the Roche limit. Carolyn Porco of the University of Arizona, Tucson, has suggested that there are 86 stable arcs around Neptune, where shepherding satellites would confine fragmental material to its ring.
When Saturn was the only known ringed planet, astronomers believed that the rings were permanent and even as old as Saturn itself. Since Voyager, however we now know that all the major planets have rings, but they are transitory, and could not be more than 100 million years old.
Saturn's rings, of which there are at least 95, are all in the equatorial plane of the primary, and prograde. The outermost ring of Uranus, the e ring, is 0.8 of the Roche radius. As I believe that each of the planets is growing in mass and radius, so must the diameter of each Roche radius, so that inner satellites should progressively disintegrate to form rings.
of Saturn's rings was first suspected by Galileo in 1610, but it was another
45 years before they were first resolved by Huygens. Resonant disturbance
by the attraction of Saturn's major satellites have swept clear prominent
gaps in the ring plane. The first such gap was discovered by Cassini in
1675. They are now called the Kirkwood gaps (Figure 116), after the man
who first explained them.
Four [Five] of Uranus' small shepherding satellites (Cordelia, Ophelia, Bianca, Cressida, and Desdemona) are a little inside the Roche limit, straddling the e ring, which is the outermost of Uranus' nine rings, so presumably their cohesion is still enough to hold them together (our man-made satellites are well within the limit, but do not disintegrate).
The fact that the Uranian rings range greatly in inclination and eccentricity, and that these variables diminish progressively inward through older disruptions, favors an origin from disruption of satellites. Ring arcs and azimuthal variability in optical depth suggest the disintegration of former satellites in more eccentric orbits.
The dynamic activity of the Uranian satellites is in order of their distance from the planet - Miranda, Ariel, Umbriel, Titania, Oberon. as the planet's gravity becomes less significant in relation to the satellite's own gravitation. Dynamic studies indicate that all the rings are relatively young and have a limited future life.
lt may be fortuitous that at our time we observe Saturn as the planet with such spectacular rings. At some time in the future Saturn's rings may have dispersed into the planet, and Uranus might have a most spectacular ring, if during last third of geologic time the disintegration of Miranda into a very spectacular ring had occurred. The expected life of a ring has been estimated as 100 million years. (For a fuller discussion, see Pollack et al., 1990)
Neptune has at least four rings, Adams (the outermost), Leverrier, 1989 N4R (yet to be named), and Galle (the innermost). There are five nearby satellites, Lavinnia, Despina, Galatea (the largest, about 80 km radius), Thalassa, and Niaid.
Dynamic analysis shows that Galatea has the most significant shepherding effect, constraining the ring particles to oscillate in their orbit in a wave pattern synchronous with Galatea. Galatea is at present a little outside the Roche limit, but if Galatea were to disintegrate in the future as Neptune increases his radius, a most spectacular ring would result.
The commonly accepted theory is that during the consolidation of the planets from a primordial gas nebula, Jupiter must have condensed quickly - in less than a million years - so that its mammoth gravity prevented the planetesimals orbiting between the present Mars and Jupiter from coalescing to form a single planet.
What was the source of the heavy saturation bombardment of the already-formed planets and satellites? The total mass of the asteroids is only 1/200th of the mass of the Earth. As early as 1803, Olbers thought the asteroids were fragments of a disrupted planet, and searched for a common perihelion to indicate the common source.
In 1982 Simon Newcomb did confirm that the perihelia of asteroid orbits were concentrated on one side of the Sun, and it is significant that the general inclination of the asteroid belt is about 10o to the ecliptic. But in 1907 Huth suggested that the single large planet was imaginary, and that these tiny planets were as old as the other planets and” had coagulated into many small spheres in the space between Mars and Jupiter”.
Huth's small spheres” were a meme of his imagination, for only three of the asteroids just reach sufficient self-gravitation to pull themselves into near-spherical shape. Most asteroids rotate rapidly between four and twenty hours, which is what would be expected from fragments from explosive disruption.
The 1772 announcement of Bode's law set off a frenzied search for a missing planet between Mars and Jupiter. Herschel's 1781 discovery of Uranus, a good genuine planet where predicted by Bode's law, deepened the mystery and led to the 1801 discovery of Ceres (soon followed by Pallas and Juno). In the predicted place, yes, but too surprisingly small to be called planets! Then one by one, thousands of others!
Jan Jarkofski (1888, 1889), the pioneer of the theory of Earth Expansion, assumed that asteroids were the remains of a disrupted planet which had disintegrated by explosion.
David Hughes (1990) has calculated that there should have been 2200 times as much matter in the asteroid region of the solar nebula as there is today. He also pointed out that iron asteroids make up 3.7% of the mass of the asteroid belt and iron meteorites make up a similar proportion of all meteorites, and that a body with 3.7% of its material in its core would be 8,600 km in diameter.
Several astronomers have concluded that Deimos and Phobos, Mars' two small satellites, are captured asteroids. Hughes even speculates whether Mars itself is an asteroid, one of a dozen of similar size, whose collisions through the subsequent three billion years yielded the present thousands of asteroids, Mars, by chance, being the only survivor.
Ovenden (1972, 1973) concluded from his study of the evolution of the resonance of the Jupiter-Uranus-Neptune group, and independently from the resonance of the Mercury-Venus-Earth-Mars-Jupiter group, that a pre-asteroidal planet, Aztex, as massive as Saturn, was implied right up to 17 million years ago (Miocene).
Ovenden pointed out that, whereas the rubidium-strontium and uranium-lead ages of meteorites are around 4.5 x 109 years, the cosmic-ray exposure ages of chondrites and achondrites lie between 2.2x107 and 5.0x 106 years, tailing off toward the younger end (upper Miocene). The resonance of the asteroidal orbits under Jupiter's helm seems to be significantly less developed than that of the solar system as a whole, in accord with the recency of the disruption of Aztex.
Guskova (1975) deduced from the remnant magnetisation of meteorites that the asteroids are the remnants of a space catastrophe which destroyed an asteroidal planet which she called Phaeton, which had a magnetic field, and which had been a little smaller than the Earth. When the Galileo spacecraft approached asteroid Gaspra in 1991, a directional change in magnetic field was recorded, apparently by Gaspra's magnetism. No conventional theory explains how a solid body with maximum radius of 15 km acquires a magnetic field. Perhaps Gaspra is entirely magnetite.
Taasch (1972) had called this asteroidal planet Aster. Evidence for frequent collisions between asteroids, yielding the several asteroid families, is not questioned by anybody, but current orthodoxy rejects Aztex-Aster-Phaeton (Chapman, 1975; Napier and Dodd, 1973) assuming instead that the present asteroid zone was originally occupied by several minor planets.
Bell et al. (1985) report that Amphitrite's spectral features indicate nickel-iron metal with a band near 0.95 microns due to pyroxene and olivine absorptions and a band at 1.95 mm due to pyroxene alone. The A-class asteroids, 246 Asporina, 289 Nenetta and 446 Aeternitas, seem to be nearly pure olivine - fragments of a highly differentiated planet.
Meteorite fragments of asteroids include irons, meshes of ultramafic minerals, and the carbon chondrite category of more hydrous rocks, which together appear to represent the zones of a large planet. It is difficult to visualize how a swarm of small bodies could differentiate into these types.
Also their Neuman lines seem to require high pressure not attainable in planetoids, as would their remnant magnetism. The range of minerals, dominated by iron, olivine, pyroxene, and tridymite, and even with rarer diamond, are strongly suggestive of the mantle and core of a planet.
Jupiter's inner system, the rings, Amalthea, and the four Galilean satellites (Io, Europa, Ganymede, and Callisto) all orbit in synchronized prograde orbits out to 1170 km. Outward from this group, there is a 6000 km empty gap, then a group of four satellites between 7000 and 7300 km with large orbital inclinations in retrograde orbits (Leda, Himalia, Lysithea, and Elara, in order of increasing distance). Then there is another 6000 km gap to four tiny pro-grade satellites also with large orbital inclinations (Ananke, Carme, Persiphae, and Sinope).
If a planet in the asteroid position with an orbital velocity of about 20 km/s exploded with radial velocity of 8 km/s, fragments shot forward would have a perihelion velocity of 29 km/s near the Sun, and aphelion velocity of about 13 km/s in the vicinity of Jupiter's orbit. They could be captured in prograde orbit if captured outside Jupiter while overtaking (Ananke, Carme, Pasiphae, and Sinope). Or they could be captured in retrograde orbit if being overtaken by Jupiter at aphelion on the inside of Jupiter.
Saturn's hundred rings could have come from an Aztex explosion if Saturn happened to be near conjunction with Aztex, and Jupiter much farther away in its orbit. Smaller Mars could only capture close encounters, and in any case could have been far from conjunction. In addition to its hundred rings, Saturn has 17 satellites including Phoebe in a retrograde orbit of 0.063 ellipticity and high eccentricity (0.749) and 150o inclination, separated from Iapetus by a 9 million km gap.
If a larger moon-embryo chunk were shot backward it would thereafter have aphelion there, and could be captured by the Earth at perihelion if it overtook Earth on the outside of the Earth's orbit. If it overtook the Earth with a relative velocity of one km/s, it would drop into orbit with little or no tectonic disturbance to the Earth, except that the Earth would experience lunar tides for the first time.
Did the Earth have a Moon before the late Mesozoic? Is the dispersion of Pangea, which began in the late Triassic, and the rapid rate of expansion since then due to Aztex explosion, Moon capture and daily gravity reduction through the Moon's attraction? Certainly, some have claimed to have identified lunar sedimentation cycles in pre-Cretaceous strata, but they had assumed that we had always had Moon.
George Darwin claimed that the Moon was born from proto-Earth through fission, but no one has explained how the daughter Moon escaped through the Roche radius. Four-billion-year isotope ages recorded from meteorites and Moon rocks could be the age of their original Aztex parent, not the age of its disintegration.
Deimos and Phobos could be fragments captured by Mars. Neptune's Nereid has a highly inclined (28o) very eccentric (0.749) orbit from 54 to 400 times Neptune's radius. Neptune's Triton, with its high inclination, retrograde orbit, and 70% rocky core-a misfit in this region-may also be a captured asteroid.
Much material would end up absorbed by the Sun, and the other planets would also absorb much. Comet Chiron could also be a remnant of the postulated Aztex explosion, and perhaps all ecliptic comets. Phoebe is very similar to Chiron, and may be the residue of a comet. Some fragments may have been lost to space.
Could an Aztex explosion be the catastrophe at the Cretaceous-Tertiary boundary leading to the "extinction” of the dinosaurs and other phenomena, the subject of current controversy?
Deep-sea micro-meteorite spheres occur in three types:
(1) stony olivine and glass;
(2) Ni-Fe sulfide, composed of magnetite, pyrrhotite. and iron;
(3) Ni- Fe metal, magnetite and wustite.
They appear to have condensed from a plasma splash projected into Earth orbit by an asteroid impact. The oceans which contain them date only from the middle Mesozoic. Could they represent the splash from the Tertiary boundary impact of an Aztex remnant?
The planet-disruption model, despite difficulties, makes good sense. But what was the source of such an explosion? The collision of two planets? That is merely an extension of the current hypothesis. If my meme is correct, that all the masses of the Universe are expanding, and that therefore all heavenly bodies are in a mass-increasing progression, there is a discontinuity across the asteroid belt from densities of 3+ to densities of about 1 g/cm3.
Current theory rules out a nuclear explosion, but perhaps an Earth-mass runaway expansion occurs (such as seen on Earth since the Cretaceous), accelerating to explosion at a couple of Earth masses, when heat is produced more rapidly than it can be transmitted out by combined radiation, conduction, and convection.
Larger bodies (Sun, Jupiter, Saturn, Neptune, and Uranus) may have been through this process but had sufficient mass to cohere again (at lower density), but at a critical mass of the alleged asteroidal planet, self-gravitation was insufficient for re-assembly. On this scenario, the Earth which has been expanding at an increasing rate for the last 100 million years, would be next (Figure 112 and 114)!
During the nova stage of tenuous gas at the birth of the solar system, all radioactive daughter isotopes were effectively separated from their parents, resetting radioactive clocks, so all bodies in the solar system - meteorites, comets, satellites and planets alike - converge on maximum ages of a little more than four billion years.
However, the Allende meteorite which fell in Mexico in 1969 contains an excess of 29Al, a radio-active isotope with a half life of 720 thousand years, which should have declined to negligible proportions in much less than 100 million years. Also the Richardson meteorite, which fell in Manitoba, has an excess of 129Xe, whose only known source is 129I, a radioactive isotope with a half life of 17 million years, which should have declined to a negligible amount in less than 200 million years. The implication is that the 29Al and the 129l were produced much more recently than the nova event which created the red giant from the proto-Sun. Was this the explosion of the asteroidal planet, Aztex?
Asteroids have been broadly classified either by their orbital parameters or by spectral type, which correlates with distance from the Sun and also to some extent with size. Spectral typing is locked into the surface of the asteroid, which may have been significantly altered by sustained micro-meteoroid impacts or by the solar wind.
S-type asteroids are the most numerous, with a gaussian distribution maximum Sun-distance at about 2 AU, are interpreted as having igneous minerals, pyroxenes, olivine, and sometimes nickel-iron; so also E-type asteroids, which peak at about 1.5 AU. M spectral types are a small group peaking at about 2.7 AU, and seem to be nickel-irons. C, B, G, and F spectral types are broadly peaked at 3 AU and are interpreted as similar to carbonaceous meteorites. P spectral types are quite numerous, with low albedo and are considered by some to be primitive. D spectral type asteroids are more abundant farther out, peaking at about 5 AU, and include the Trojans, which share orbits with Jupiter.
Some consider that the early Sun passed through an active T-Tauri phase with a dense powerful wind which induced strong electric currents, that differentially heated asteroids. The greatest effect was in small asteroids (20-40 km radius) bodies at moderate distance from the Sun (S-type asteroids) (Mckinnon, 1989).
In 1772, Lagrange showed that a system of three mutually gravitating bodies was stable in the special case where the three formed an equilateral triangle, so that asteroids would be stable if they were in Jupiter's circular orbit and 60o ahead of Jupiter or 60o behind Jupiter with respect to the Sun (Figure 117). This simple picture is somewhat complicated by the interfering attraction of Saturn, by the fact the Jupiter's orbit is elliptical (eccentricity 0.03 to 0.06) not circular as implied for the Lagrange stability, and also by variation in the inclination of the Trojan asteroid orbits.
As a result, the Trojan asteroids librate by as much as 40o about the simple Lagrangian points. Some 700 Trojans larger than 7 km radius, named after Greek heroes, precede Jupiter, but only 200, named after the heroes of Troy, follow Jupiter.
Lagrange-stable bodies in the orbits of Saturn and Earth have not found
any substantial body, but the zodiacal light has been attributed to dust
particles in Earth orbit about the Lagrangian stability.
Most asteroids have stable orbits between Mars and Jupiter, but thousands of them have orbits which bring them inside Mars; Earth, Venus and even Mercury at perihelion. There are three groups of Earth-orbit crossers: The Apollo group of 46 known members cross the Earth orbit to a perihelion well inside the orbit, but have larger maximum semiaxes so that their aphelia are well outside.
Four are known to have inclinations greater than 40o and fourteen have inclinations between 15o and 40o. Some of the 47 Amors may graze the Earth, but their perihelia are mostly outside Earth's aphelion. They form a continuous distribution with the Apollos, the criterion being whether the perihelion is less than or greater than that of the Earth.
the orbit of Mars. The seven Atens have perihelia and major semiaxes less
than those of the Earth. Three have inclinations greater than 15o.
Members of the Apollo-Amor-Aten group have the potential to collide with
the Earth at some stage, and there are certainly many more which are too
small to have been seen so far.
The 144 member Eos family is a compact group with high inclination, with 221 Eos1 (49 km radius), 579 Sidona (40 km), and 639 Latona (34 km). Their immediate parent before disruption was at least 90 km in radius, orbited at 3 AU, and suffered relatively early disruption.
Subsequently the number of such families has grown to nearly thirty. The Themis family (165 members): 24 Themis (125 km radius), 90 Antiope (69 km radius); the Eos family (144 members), Koronis family (86 members); Cybeles (51); Hildas (34); Phocaeas (62); Trojans (35); Apollo-Amor-Aten (36); Floras (429); Hungarians (30); Mars crossers (29); Nysas (44); Pallas Zone (4); Griquas; Budrosa family(124); Concordias (132); Meliboeas (113); Letos (124); the Alexandros (138); the Main Belt I (316); the Main Belt IIa (455); Main Belt IIb (298); Main Belt IIIa (189); and the Main Belt IIIb (480).
The 100 member Themis family, centered on 3.14 AU, has small inclination but large eccentricity. The largest members are 24 Themis (125 km radius) and 90 Antiope (69 km). The immediate parent must have been at least 150 km in radius.
The Nysa and Hertha families are close neighbors, separated by a narrow gap in inclination near to the 1:3 resonance with Jupiter. The largest are 135 Hertha (35 km radius) and 44 Nysa (33 km ). A parent body of about 100 km radius is hypothesized.
The 86-member Koronis family has small inclination and small eccentricity in the main asteroid belt between 2.8 and 2.9 AU, between the 5:2 and 7:3 Kirkwood gaps swept clear by Jupiter. The immediate parent would have been some 45 km radius, which seems to have suffered relatively late disruption.
The Hilda family of 31 members may be in part captured comets (at about 3.9 AU much farther out than the main asteroid belt) librating at near 3:2 resonance with Jupiter, with low to moderate inclinations. The still smaller Thule family is further out in low eccentricity orbits at 4.25 AU in 4:3 resonance with Jupiter.
The Flora family centered on 2.25 AU is the largest group with 429 listed members of which 8 Flora (80 km radius) is the largest. Flora itself is nearly equidimensional (within 10% of spherical) but is too small for self-gravitation to have formed a spherical shape.
The Undina family contains 94 Auora (95 km radius), 92 Undina (92 km), and 490 Veritas (63 km), for which a 136 km radius parent is assumed. The Muliboea family contains 137 Meliboea (76 km radius) and 788 Hohensteina (61 km), thought to be derived from disruption of a 105 km parent. The Budrosa family contains 349 Dembowska (72 km) and 558 Carmen (32 km), thought to be derived from disruption of a 190 km parent.
The Leto family is led by 68 Leto (64 Km) and 236 Honoria (34 km), derived from disruption of a 100 km parent. The Concordia family consists of 128 Nemesis (95 km) and 58 Concordia (52 km) derived fram a 125 km parent:
The Alexandria family consists of 54 Alexandria (186 km) and 70 Panopaea (76 km) derived from a 135 km parent. The 190-member Hungarian family is the innermost of the main belts of asteroids apart from the Earth-crossers, occupying the l.8-2.0 AU region.
944 Hidalgo has its aphelion near Saturn, and perihelion just outside Mars, so its orbit is more like that of a comet than an asteroid. Chiron, first classified as asteroid 2060 has its aphelion beyond Saturn's orbit, but has since turned out to be a comet.
3200 Phaeton is in the orbit of the Geminid meteor shower stream, generally regarded as a former comet orbit. Could other ”asteroids” be dead comets? This has been suggested for, some of the Earth-crossing asteroids. If asteroids are indeed related to cornets, the link would be the other way-comets may be the extreme distant end of the asteroid distribution.
Comets are short-lived small bodies in highly eccentric orbits, with perihelion near the Sun and aphelion near the limit of the solar system, and with usually high inclination to the ecliptic. They may approach 3 km in diameter, but are commonly less than a kilometer.
The name is derived from the Greek [word for hairy] because they generally have a tail, which resembles a beard when the comet is receding. Comets are named by the year of discovery and the name of the discoverer or up to three discoverers. This restriction is necessary, because some bright comets are discovered simultaneously by many observers.
Orbital inclination and eccentricity have been determined for more than 500 comets, mostly telescopic. Most of these are long period comets with random inclinations and periods more than 200 years; they not known to be periodic, there are as many retrograde as prograde, and orbital ellipses are less common than parabolas.
In contrast, the hundred or so short period comets in elliptical orbits are mostly prograde with inclinations less than 30o. This suggests that there may be two categories of comets, long-period interstellar strays which are random intruders to the solar system, and the other category which are definitely part of the solar system, and come from the Kuiper belt of planetesimals which extends outward beyond Pluto.
Comets are believed to consist of solid particles in a matrix of volatile icy materials, which tend to volatilize as they approach within some 3 AU of the Sun. From such distance, whether approaching or retreating, the nucleus forms a bright coma, which may extend as much as a million kilometers.
When only 2AU from the Sun, a bright luminous tail is drawn out along rectilinear lines for l0o to 40o (107-108 km) not in the direction of motion, but in the direction of the solar wind, pointing away from the Sun.
Sometimes there are twin tails, flowing away from the coma at a speed of 2000 km/hour, one mainly luminous dust particles, and the other a plasma of electrons and ionized radicals. The 1744 Cheseaux comet had six tails! The Great Comet of l843 had a plasma tail extending over 2 AU, a quarter of the sky. Sometimes the tail has knots and kinks which move out along the tail at speeds of 10-200 km/s.
The coma of at least three comets at 1 AU from the Sun have been found to be surrounded by a cloud of atomic hydrogen 10 million kilometers in diameter (larger than the Sun) streaming out of the coma at 8 km/s.
Spectroscopic studies have recorded in the coma elements : H, O, C, Na, K, Ca, V, Fe. Cr, Co, Ni Cu, and Mn, and many compounds and radicals and ions: OH, CH, CN, CO, CS, HCN, CH3, CN, CH3CN, NH, and NH2.
The spectrum of a comet shows that the light is partly reflected sunlight, and partly original. Water, which is considered to be a major constituent of the nucleus, has not been observed in the spectra. Nevertheless the” dirty snowball” model with water ice the main part, is still the creed. Is this an earthling meme?
Apart from the small nucleus, the matter of which the comet is composed is very bright but extremely tenuous. Stars have often been seen through even the thickest parts. Sir John Herschel reported that in 1832 he saw a group of stars of sixteenth magnitude through almost the centre of Birla's comet. The Earth has passed through the tail of a comet without any observable effect.
Comets are short-lived because they lose about a meter of their surface by evaporation at each passage around the Sun. About ten comets appear each year, with one spectacular enough to attract the naked eye.
The nucleus of a comet slowly dissipates and may eventually disintegrate. Sekanina studied data on 21 split comets. When comets split they separate slowly through sublimation jet thrust. The Shoemaker-Levy comet broke up into a” string of beads” along the orbit, and impacted Jupiter in June 1994.
Like asteroids, comets also occur in families of similar inclination. The first person to calculate the orbit of a comet, was' Edmund Halley in 1680, using the new gravitation law of his friend, Isaac Newton. He noticed the 'striking similarities of his orbit to the comets which had appeared in 1531, 1607, and 1682 and concluded that these were the same comet with a period of 75 to 76 years, and predicted that it would return in 1758. The subsequent returns of this comet were in 1835 (observed by the famous mathematician, F. V. Bessel), 1910, and 1985.
The 1066 return of Halley's comet was recorded in the Bayeux tapestry, credited with having heralded the Battle of Hastings. It is said that Halley's comet was the one recorded by the Chinese annals as having appeared in 240 and 87 B.C. Halley's comet is retrograde, eccentricity 0.967, with perihelion of 0.59 (between Mercury and Venus), and aphelion 35 AU (between Neptune and Pluto).
Like Halley, T. F. Encke computed the elliptical orbit of a faint 1819 comet and showed that the same object had been observed in 1895, 1795. and 1786, and predicted its return in 1922. Encke's comet has the shortest recorded period, returning every 3.3 years, although at its brightest it is a little below the limit for the naked eye.
At each perihelion Encke's comet loses 0.2% of its mass, so that its orbit is becoming progressively smaller and more circular. It is now two magnitudes fainter than it was 100 years ago, and the period has decreased by two days, and is expected to disappear by the year 2000.
Rainfall statistics over more than a century show that comet orbits are associated with meteor swarms (“shooting stars”) on the dates that the Earth crosses comet orbits, and that increased probability of rain follows 30 days later Meteor showers are named for the point in the sky (known as the radiant point) from which they appear to emerge. Halley's comet is associated with the n-Aquaiids in early May (ascending node) and the Orionids in late October (descending node).
Encke's comet is responsible for the Taurid October swarm and the daytime B-Taurid shower in late June. Other prominent meteor showers are from the Pons-Winnecke comet (June), the Giacobini-Zinner comet (October), and the Leonids (November 16). The dust in comet orbits is certainly very hydroscopic.
2101 Adonis is associated with meteor streams and may be an extinct comet. 2201 Oljato is associated with several meteor streams.
Some asteroids like 1983 SA, 1983 XF and 1984 BC are in cometary chaotic orbits. l983 VA, 1982 YA, 1983 SA, and 1083 XF may also be extinct comets. Shoemaker regards Hidalgo (38 km radius) as an extinct comet. There is a dynamical similarity between some comets and some Trojan asteroids.
In 1950 Jan Oort postulated that comets came from a vast spherical cloud more than 104 AU from the Sun, still weakly bound gravitationally but occasionally perturbed by passing stars to be either ejected from the solar system or diverted into the inner solar system with a perihelion near the Sun and an aphelion among the outer planets. This is still the standard creed, but its validity is not established. Its weakness is the lack of ”passing stars” in times sufficiently short geologically to account for the frequency of comets. The hyperbolic intruders do not fit, and the lack of spectroscopic confirmation of water casts doubt on the” dirty snowball” model.
Kuiper suggested that a belt in solar orbit between 30 and 50 AU, just beyond the orbits of Neptune and Pluto was the source of comets with periods less than 200 years. More recently David Jewitt of Hawaii and Jane Luu of Harvard have estimated that the Kuiper Belt may contain 35 thousand minor planets larger than 50 km radius (that is many more than in the Asteroid belt).
A glowing fireball or ”shooting star” is a meteor. It it survives the ablation of passage through the atmosphere, and reaches the ground, it is a meteorite. Meteorites are classified as irons, stone-irons, and stones, depending on the relative proportion of iron alloy and silicates.
Meteorites are the small end of the asteroid size continuum. Carbon chondrites are common in witnessed falls, then come stones. Iron meteorites, although less numerous than stones are much stronger and more resistant to weathering, and more conspicuous, so irons predominate among ”finds”.
Meteorites represent a rare event, as less than 3000 meteorites are known, apart from tectites, which are wholly-melted glass globules which are found in thousands as ”strewn fields”, and microtectites which are solidified drops, found in large numbers in some marine sediments.
By contrast, meteors are extremely abundant, and may be witnessed on any dark night, when not dimmed by moonshine or city glare. They are more numerous on particular dates which repeat annually when the Earth crosses comet orbits. The Earth receives an annual addition of 108 kg of meteoric matter.
The standard creed is that some meteorites had individual existence right from the primordial gas cloud which became the solar system, but the majority of them are fragments of asteroids disrupted by frequent collisions, themselves fragments of the former asteroid planet. Meteorites occur in all sizes from asteroids themselves, hundreds of kilometers in diameter to mini-asteroids, down to interplanetary dust. Radiometric ages indicate that their material consolidated thousands of million years ago, at the time of the formation of the solar system, but their surface exposure ages are very much younger, peaking in the Miocene. They become diverted into the vicinity of the Earth by mutual collisions, and gravitational deflection by planets, particularly Jupiter.
Both asteroids and meteorites provide samples of the deep interior iron core, the pyroxene-olivine mantle, and the carbonaceous hydrated mantle of a disrupted planet. So far as I know, carbides and hydrides are not represented.
Meteorites enter the Earth's atmosphere at 150 km altitude as angular objects, with speeds of 20 to 40 km/s. A brilliant fireball is visible over a region some 500 kms in diameter followed by the sonic boom. Ablation commences immediately, leaving a luminous trail, with rapid deceleration toward terminal free-fall speed.
If it has not been consumed by a height of some 20 km, it may impact the ground. Small meteorites may not dent the ground at all, but large ones will burst a crater. This is a question of mass per unit surface (Stokes' law).
The terminal speed of tectites is not much greater than hailstones. Iron meteorites commonly survive intact, but stones usually fragment, and fall along the line of flight, the largest first to the smallest (most retarded) in line back towards the entry point. Stones are often pocked by gas emission.
The melted surface is very thin, and quickly cools because the interior is very cold, so a newly fallen meteorite is not hot to pick up, except at the rear where ablated matter has gathered. If left in moist air, a coat of frost may quickly develop. The surface is usually black (fused iron silicate).
A large meteorite still has most of its entry kinetic energy on impact and the whole of this is dissipated in a few seconds-enough to convert its own mass and an equal mass of the country rock to a rapidly expanding plasma.
The crater of a large meteorite resembles that of an atomic explosion. The close-in central zone becomes a plasma, surrounded by a zone that has been volatilized, then a zone that has been flash melted to black glass, then a zone of blue-grey powdered rock, then a zone of radial slickensides with shock recrystalisation, then a zone of strong shear jointing, beyond which the shock is transmitted radially outward as seismic waves.
Morphologically, there is a central caldera several times the diameter of the impacting body, with walls at the angle of rest that have suffered late gravity collapse, covering an upturned, perhaps overturned, rim, then a wide flange of the fractured rock ejected from the crater, often with distinct radial rays. The crater has a negative gravity anomaly.
A bonanza was found in Antarctica in 1969 when more than a thousand meteorites were recovered from the surface of glacier blue ice, where they had been preserved in ice and snow without any contamination, as the advancing glacier moved them forward.
More than 100 different minerals have been recorded from meteorites, a quarter of them found only in meteorites. A wide spectrum of meteorites has been studied, but broadly they fall into three categories: irons, chondrites, and achondrites, according to whether they contain chondrules - spherical bodies consisting of olivine (with spinifex texture, pyroxene and glass, in a finer matrix. Some irons also contain chondrules.
There are half a dozen categories of iron meteorites, mainly according to the amount and structure of kamacite (nickel-iron, also called alpha iron). Hexahedrites contain 5 to 6.5 % nickel while octahedrites contain more, up to 16%. Iron meteorites may enclose crystals of olivine, bronzite, or tridymite.
Most irons have Neuman lines (unknown in terrestrial rocks) which show up when the polished surface is etched with nital, a solution of nitric acid in methyl or ethyl alcohol, that attacks the nickel-iron phases differently. Anatexites are fine-grained iron meteorites with higher nickel content with taenite (gamma nickel-iron) and schreibersite (Fe,Ni)3P
Among the chondritic meteorites, the silicates in the chondrules, which may be pure enstatite, or various combinations of olivine, bronzite, hypersthene, or pigeonite, equilibrated with the matrix. The nickel content may range from 0 to 12% when pentlandite substitutes for troilite. In unequilibrated chondrites, the chondrules differ markedly from a crumbly matrix.
Chassigny and Brachina are examples of pure olivine meteorites - a differentiate product of crystal settling in a larger body. Their spectra closely match those of asteroids 146 Asporina and 289 Nenetta (Chapman, 1984); pyroxene would have shown up if it exceeded 10%.
Carbonaceous chondrites are an important category with up to 4% carbon in complex compounds, and a considerable content of water as hydrous sulfates and silicates. Free sulfur may be present. Unless they are seen to fall, carbon chondrites may not be recognized as meteorites, although they are a common kind.
Achondrites are coarsely crystalline, resembling terrestrial rocks such as dunite, peridotite, or basalt. Minerals may be olivine, enstatite, calcic feldspar, diopside, or augite, with minor accessory minerals such as iron (with low nickel), graphite, and occasionally small diamonds.
Decay products of two extinct isotopes, 129I and 244Pu, with half lives of 1.6 and 8.2x107 years respectively, have been reported from some meteorites and are also present in lunar samples and mantle xenoliths from the Earth, interpreted as indication that the Earth, Moon, and the parent body of meteorites were all formed soon after the cataclysm which formed the solar system.
The mineralogy and texture of meteorites imply the equivalent of Earth's deep mantle pressure, which could not be attained in the small parent bodies postulated as the source of asteroids and meteorites. Nor could the differentiation of a primitive gas cloud yield, some bodies of pure nickel iron, others of chondritic minerals, and still others, like the carbonaceous chondrites. Late disintegration of a pre-asteroidal differentiated planet of Earth-like dimensions is implied.
Some have suggested that meteorites were the source of life on Earth. Certainly the essential elements (carbon, hydrogen, nitrogen, and oxygen) do occur in meteorites, along with some key carbon compounds such as amino-acids, but these are optically racemic. Biological compounds on Earth are levorotary, thought to be due to the destruction of dextrorotary isomers by bacteria. Environmental conditions on Earth were favorable for the development of primitive life, whereas the reverse was so in the meteoric environment. A pre-asteroidal planet would not help, because its disruption and possible Earth seeding, would have come too late.
Cratering is universal through the solar system, but on the large ”gas planets” impacts are not recorded, so we are confined to the terrestrial planets and all satellites. The first question is the separation of impact craters from endogenic craters. While some are identified as volcanic, the vast majority are accepted as impact scars.
Craters on Moon have been known since Hariot and Galileo observed them with telescopes in 1609, but were interpreted as volcanic. Only in 1994, was the largest of all been recognized - South-Pole Aitken Crater - reported in the December 16 issue of Science, by Maria Zuber, to be 2500 km in diameter, 16 km deep (Moon's deepest) and estimated (by crater count) to be some 4 billion years old. The far side of Moon is cratered to saturation, that is, with continuing bombardment does not increase crater density.
By contrast, the near side of Moon has several large old craters some 4 billion years old, flooded with lava-Imbrium, Tranquilitatis, Serenitatis, Crisium, Orientale, and Frigoris. Thousands of younger craters overprint these, right up to the youngest, like Archimedes and Copernicus, whose radial ejectamenta rays extend for hundreds of km.
Mercury is cratered to saturation, ranging from the smallest that can be resolved (about 100 m) to multi-ringed craters hundreds of kilometers across, by convention called `basins', Caloris, the most prominent is so-named because of its location at Mercury's hot spot which receives maximum insolation (adopted as 180o longitude). The smooth plains in Caloris and between the rings are interpreted as due to later volcanism, followed by many more small crater impacts. Radar images of the unseen hemisphere indicate craters up to 800 km. Mercury's surface looks like Moon, grey and heavily cratered to saturation. Assuming Moon dating applies to Mercury, the, bombardment peaked some 4 Gy ago.
Many Mercury craters have several concentric rings: Caloris, has rings of 630, 900, 1340, 2050, 2700 and 3700 km diameter; Tolstoj, three rings to 2230 km; Borealis four rings to 720 km; and there are 18 other multi-ringed craters, and hundreds of craters dawn to saturation at the limits of resolution. The large craters were subsequently flooded by lavas. The youngest craters have sharp crisp rims scalloped by inward landslides and have bright rays and ejectamenta, but older craters have been progressively blurred by later impacts.
Venus is extensively cratered, but has only large ones. The numerous smaller bodies which would have blasted sizeable craters on the Earth all burned up in the thick atmosphere, and even quite large ones were so disaggregated by the atmosphere that they formed recognizable ”splotches” on the surface hundreds of kilometers in diameter Venus' crater distribution is unimodal without significant regional variation.
Schaber et al. (1992) suggest that asteroids less than a kilometer in diameter would not reach the surface, but would form a shock wave of more than 1 kbar pressure at the surface. Splotches ranging up to 200 km in diameter are present on quite old surfaces, implying that the Venusian atmosphere (and the resulting high surface temperature) is primitive.
Perhaps this explains the lack of water, for unless magmas are very different from the Earth's, water should have been brought to the surface perennially throughout the ages.
Chapman (1973) stated that the largest craters on Mars are substantially degraded, medium-sized craters are filled to intermediate degrees, and the smallest most easily eroded craters show little evidence of modification.
Puck was photographed (about ten pixels wide) by a near passage by Voyager II. Puck (only 75 km radius), orbiting Uranus at 86,000 km, has three large impact craters, Bogle about 50 km across and Lob and Butz some 10 km, and several smaller ones, which appear to belong to the early cratering period of the solar system.
Phobos (only 20 km radius) has extensive large impacts, although these may have occurred before capture by Mars. The largest is Stickney, some 10 km in diameter. Trailing across the surface from near Stickney are long parallel grooves and ridges 100 to 200m wide and about 20 in deep, which have puzzled astronomers since their 1976 discovery by a Viking spacecraft. But Murray et al. (1995) have satisfactorily explained them as secondary debris streaks from primary impacts on Mars. The largest crater on Deimos is about 2 km across.
Enceladus is moderately covered by craters up to 35 km in diameter, older craters having been buried by volcanic” resurfacing”, but some have suggested that Enceladus could be the source of Saturn's E-ring particles, possibly ejected during a major impact. Mimas is heavily cratered, the largest being Herschel 30 km in diameter, which has a central peak.
Tethys is crater-pocked to saturation, Odysseus being 400 km in diameter. Dione is heavily cratered on the leading face, but less so on the dark trailing face, which seems to have been resurfaced. Rhea's surface is totally saturated with craters, so that new impacts obliterate as many old craters as new ones they create. The largest remaining craters are about 300 km in diameter, but larger older ones may have been obliterated..
Titania has few large craters but an abundance of small ones, apparently because the earlier fields were covered by global volcanic resurfacing. Gertrude, the largest, has a rim diameter of 303 km with a wide apron of moderately cratered terrain. Oberon's craters include simple bowls and some more complex with flat floors, central peaks, and prominent ejecta blankets.
The surface of Umbriel is heavily cratered. Io has been completely covered by recent flows of sulfur of different hues.
Callisto's surface is cratered to saturation. Larger old craters are recognized only by palimpsests, the largest, Regio Galileo, being about twice as large as India, half the diameter of the satellite itself. The central bright region is 300 km across and the surrounding fracture rings extend out 1500 km. Despite the intense cratering and the wide ring system, relief is very subdued, although obviously very old. Cratering is spread over a long time, because there are some palimpsests as well as very young craters on young bowl-shaped craters.
Ganymede is heavily cratered with well developed ejecta blankets with some lobate flows, and some sharp-rimmed craters with rays.
As every body of the Solar System, even tiny ones like Phobos, has suffered intense impacts, Earth certainly had a similar fate. The 1908 Tungusta event in Siberia is the most recent, but 150 impact craters have been recorded in land areas. Erosion has rubbed out most the record, and sedimentation has concealed much more.
Many believe that extinctions at the Mesozoic boundary were caused by asteroidal impact, pointing to the 300-km diameter Yucatan Chicxulub crater. Much evidence, including iridium anomalies, exists for asteroidal impact at this time, hut I doubt many of the claims of the world-wide effects. Besides, the Chirxulub crater is too old.
Certainly, as asteroidal impact would produce a crater where the entire impacting body and a similar muss of the Earth would be instantaneously volatilized, even converted to plasma, and impact effects would propagate at super-seismic speed. But the kinetic energy would rapidly be consumed as the area of the propagating surface increased in proportion to the square of its radius. The plasma zone would be surrounded by a zone of volatilization, then of melting, then pulverization, surrounded by a zone of impulsively overturned strata, then a zone of brecciation and shear-shatter cones, until the zone was reached where the stress to be transmitted dropped below the shear strength of the rocks, after which the impact energy would propagate as seismic waves, travelling several times around the Earth.
The Richter energy scale is commonly stated to be open-ended, but elastic stress cannot exceed the shear strength of the rocks. At this stage the propagation front could be a thousand kilometers from the impact. There would of course be caustics from wave interference. The claim by some of intense antipodal effect (for example, the vast Deccan lavas antipodal to Chicxulub impact) must be false, for the stress levels would be orders too low to cause vast melting when the propagation front had travelled 10,000 km.
A marine impact would produce huge soliton tsunamis, which would cross the widest ocean with profound disturbance of sediments to a depth equal to the tsunami wavelength. Intense atmospheric turmoil would occur locally, but propagated as pressure waves. Rainfall would be limited by the amount of water available to be lifted above freezing heights, intense locally, but not globally.
To summarize, craters were initially regarded as volcanic. Modern orthodoxy interprets them as mostly impact scars - an easy option. Perhaps the pendulum has swung too far. Critical discrimination would then be needed to differentiate.
That the solar
system is highly resonant was first indicated in 1772 by Johann Daniel
Titius and publicized by Johann Elert Bode, editor of Astro-nomisches Jahrbuch,
so that it became known as Bode's Law (see table below).
first spotted the geometric progression, the planets were only known as
far as Saturn, and the asteroids were unknown. An intensive search for
the missing planet between Mars and Jupiter ensued, and to the surprise
of all, the minor planet Ceres turned up as the missing planet, closely
followed by Pallas and Juno. When Uranus was discovered, it fitted precisely.
Neptune and Pluto were apparent misfits, but if regarded as a binary the
fit is good, as is the fit of the Earth-Moon binary.
Mars and Jupiter are locked into 1:12 resonance, and Jupiter and Saturn are in 5:2 resonance, Saturn and Uranus 3:1, Uranus and Neptune 2:1, and Neptune and Pluto 3:2. Where these resonances are not precise, which happens when three bodies are involved, a libration occurs about the conjunction point.
The resonance symphony extends to the Kirkwood gaps between asteroid orbits, and the gaps between Saturn's rings through resonant perturbations of Saturn's three inner satellites, Mimas, Encelades, and Tethys (because they are so close and pass so frequently), and Saturn's largest satellite, Titan, (because it is so massive).
The most conspicuous dark gap, nearly 5000 km wide (the Cassini division between the A and B rings) corresponds to orbital periods straddling eleven hours, which is half that of Mimas (22.62 hours), one-third of that of Encelades (32.88 hours), one-quarter of that of Tethys (44.30 hours) and one-fifth of that of Dione (65:68 hours). Franklin and Colombo ( 1970) have successfully reproduced all the rings and their divisions by this resonant model.
The orbit of
the asteroid Toro projected on to the plane of the ecliptic along
with the orbits if Venus, Earth, and Mars is shown in Figure 120 which
indicates that Toro crosses Earth's orbit in January and August; but as
the revolution period of Toro is 1.6 years, five Toro revolutions equals
eight Earth years.
At the August encounters (the ascending node), Toro is ahead of the Earth and travelling faster, and hence its orbital velocity is retarded by the Earth's gravitation, reducing its momentum and angular velocity, so that the subsequent January encounters are closer. In the descending node (January en- counters) Toro is behind the Earth and is accelerated, its period is increased, and again the closeness of the January approach is increased. The result is that Toro has been captured by the Earth in a five to eight orbit-resonance cycle.
oscillates between 1.598 years and 1.602 years over a cycle of 144 years,
during which time it varies between a closest approach of 0.15 AU in August
and a similar close approach 72 years later During this period, Earth appears
to Toro to oscillate between the two close positions shown in Figure 121.
Although Jupiter is 317 times as massive as Earth, its closest approach to Toro is very much farther away, so its gravitational effect is relatively trivial. Hence although Toro is currently in safe resonance with the Earth and Venus, eventual impact with Mars, the Earth, or Venus is probable, more likely Venus, because its approach to Venus is always when both are near perihelion, when they are travelling in parallel for a significant time.
The depiction of Toro's orbit about the Earth or Venus in Figures 121 and 122 is no different from showing the Moon in nearly circular orbit about the Earth, whereas the Moon's orbit is nearly elliptical about the Sun (Figure l22).
The rotation of Deimos and Phobos is synchronous, with their longest axis pointing toward Mars, so that their rotation is about the maximum moment of inertia. Moon in synchronous rotation with the Earth, is a binary with the Earth, from which it is retreating at 3 cm/year by tidal drag. Io is tidally locked to always present the same face to Jupiter. Callisto and Ganymede are tidally locked in synchronism with Jupiter.
Europa is in resonance with Jupiter, but also completes two orbits for every one of Ganymede, and Io completes two orbits for every one of Europa, hence an oscillating tidal bulge. Hyperion is in synchronous rotation with Saturn and 4:3 resonance with its neighbor, Titan. Uranus' satellites (Miranda, Ariel, Umbriel, Titania, and Oberon) are all in synchronous rotation.
Neptune and Pluto are in 3:2 resonance (Figure 119). Their orbits regularly intersect, and they approach within 18 astronomical units, but, according to Cohen and Hubbard (1965), they should never collide. Never? Not according to application of Newtonian rules to reiteration of their reported motions. But trivial errors may magnify, and other players (such as Jupiter, Saturn, and perhaps an exotic) may modify the orbits, so it is probability rather than certainty.
Charon is so large relative to Pluto, and so close (16 times closer than the Moon is to Earth) that they are really a binary couple, each with an 8-hour period, seen edge on from the Earth twice during Pluto's 248-day” year” , so that Charon transits and is occulted by Pluto every 3.2 days. Charon is only 11 times further from Pluto than their combined center of mass.
Origin of the Moon
The Earth -Moon system is unique in the solar system in several respects, which imposes constraints on theories of origin:
(1) The Earth is the only planet with comparatively so massive a satellite - e.g.: 1/81, compared to 1/22,200 for Io, 1/12,500 for Ganymede, 1/22,200 for Callisto, and 1/4,700 for Titan. A possible exception is remote Charon, which is about 1/300 of the mass of Pluto, but not much is known about that pair.
(2) The angular momentum of the Earth-Moon system is anomalously large. The Moon's orbital inclination to the ecliptic (5.1 degrees) is anomalously high.
(3) The Moon is grossly depleted in all volatile elements. The Fe0 content of surface rocks is double that of Earth's mantle.
(4) The Moon's bulk density (3.34 g/cm3) is low compared with the Earth (5.52) hence the suggestion that Moon is stripped Earth mantle, But Moon's mass and density are consistent with her class:
(6) The Moon currently retreats from Earth at 2 m per century owing to mutual tidal drag. Such retreat projected back to the Early Proterozoic, is inconsistent with the recorded fine lamination and sediment cycles through vast thickness of the Banded Iron Formation because seiches and tidal wave caused by daily passage of a nearby Moon would disrupt such calm sedimentation. The Earth-Moon marriage must have been more recent and not catastrophic.
Hence, several special theories have been advanced for the origin of the Moon:
(a) The Moon is a captured asteroid from the disruption of the inferred planet Aztex.
(b) The Moon originated through fission of the Earth through resonant build-up of the tidal bulge, as first proposed by George H. Darwin in 1879. The Moon would have been derived from the Earth's mantle, which fits density, but misfits badly on the Moon's severe depletion of volatile elements, and fails to fit the moment of inertia, and the inclination of the lunar orbit.
(c) The Earth and Moon are individual independent planets which coalesced into a binary relationship. The geochemistry of the Moon misfits badly, which requires that the Moon be derived from part of an already differentiated body. Dynamic elements do not fit either. The Moon and the terrestrial planets were bombarded by major meteorite streams before 3.8Ga, but no direct evidence of such impacts on the Earth has yet been observed, although rocks of this age are known (Moorbath, 1977) - weak circumstantial evidence.
(d) The Earth was impacted obliquely by a Mars - sized body during the late stage of the accretion of the terrestrial planets, which resulted in the Earth-Moon system. This theory, originated by Ringwood (1986) and developed by Newsom and Taylor (1989), is currently favored by the establishment, but is denied by (6) above.
Every body in the solar system, from the very smallest observed (like Deimos) to the largest with 1000-km craters, establishes without doubt that violent collision was rife in the early history of the system. Dating of lunar rocks, if valid, indicates that the impact intensity peaked about 4.5 billion years ago.
I now attempt an eclectic summary of the solar system, my personal meme. The solar system originated from the nova explosion nearly five billion years ago of the proto-Sun; then about half Sun's present mass, with radius extending at least two astronomic units. The proto-Sun was a binary, which was responsible for the planar ecliptic, and for the distribution of angular momentum.
Alpha Centauri may have been the proto-Sun's original partner.
As condensation developed, the original planets were Mercury, Venus, Earth, Mars, Aztex, Jupiter, Saturn, Uranus, Neptune, and Pluto.
The mass of each body in the solar system and each star in the Universe has increased according to an empirical law.
Bodies less than 200 km radius do not have sufficient self gravitation to force them to creep to geoidal shape.
Bodies larger than 1019 kg have sufficient self gravitation to develop a spherical figure. They have global tensional fault patterns, show the first signs of volcanism and may retain a thin atmosphere.
Bodies larger than 1022 kg mass tend to retain some atmosphere, volcanism is well developed, and have a weak magnetic field, the origin of which is still problematical.
At they reached a mass 1025 kg a transition explosion occurred, but all except Aztex had sufficient self gravitation to recondense at a lower density (less than 2 g/cm3). When Aztex reached the critical transition mass, it disintegrated, but lacked sufficient self-gravitation to recondense, resulting in the asteroids, centered on the original slightly inclined orbit of Aztex. Asteroids and meteorites have mineralogy similar to different parts of a large highly differentiated body.
The range of asteroids and meteorites includes irons, stones, and carbon- and water-bearing bodies, representing differentiated zones of Aztex. Nobody has explained how fully differentiated iron, stone and carbonaceous minor planets could have developed from the primitive plasma between Mars and Jupiter.
Larger bodies (Sun, Jupiter, Saturn, Neptune, and Uranus) had already disintegrated, but had sufficient self gravitation to cohere again (at lower density) but at a critical mass of the alleged asteroidal planet, self gravitation was insufficient for reassembly (Figure 124).
The early period of intense bombardment of all bodies in the system is the result of Aztex's disintegration.
Mars' Phobos and Deimos, Jupiter's two outer zones of satellites, Saturn's Phoebe, Neptune's Triton and Nereid, and possibly also the Pluto-Charon pair, the elliptical-orbit category of comets, and possibly the Moon, were captured fragments of Aztex. Much of the original Aztex was captured by the Sun and the planets, and some escaped the solar system. Many satellites of the planets fit well as captures. Could all the planetary satellites have originated in this way?
Bodies larger than 1025 kg become net radiators.
As the outer planets logarithmically increased their masses, their Roche radius progressively overtook their inner satellites, which disintegrated to form rings. Such rings are transient - the inner ones being progressively absorbed by their parent planet, and new ones forming as satellites progressively disintegrate.
The cyclic repetition of orbits and rotations through so many cycles has produced a high degree ot resonances between the primaries and all the secondary bodies.
In the earliest stage, Earth is shown already solidified and pocked by craters. In the next stage the lithosphere is patterned by expansion polygons (like Mercury) with diapiric rims and broad basins in which water is already being retained. The next stage shows an equatorial rift system (like Mars) which becomes a through-going diapiric orogenic system. By the Cambrian the Caledonian-Appalachian-Tasmanide belt has become equatorial, and the present continents can be identified.
What could this imply for the future? We can only speculate. If the Earth has doubled logarithmically in the last couple of hundred million years, a runaway prospect should not be far ahead! Assuming the planets to be a consistent series,
Solar System in Geology
If the planets of the solar system, far from being passive partners, have a tumultuous history during geological time, we should now then study stratigraphy for effects there of planetary events.
The contemporary concept of an asteroidal impact at the Mesozoic-Tertiary boundary is a beginning. Major changes of obliquity of our lithosphere in the Middle Devonian and during the Tethyan orogenesis suggest a planetary cause, and recall the bizarre obliquity of Uranus, and the near absence of rotation for Venus.
Was there a relation at the Mesozoic-Tertiary boundary, of the disruption of Aztex, the origin of asteroids, the capture of the Moon, the 50o shift in lithosphere obliquity, rapid expansion with rupture of the crust with the vast mantle floods of the Semail, Troodos, Owen Stanley, and so many other ophiolites, the Tethyan diapirism and the Tethyan inter-hemisphere torsion?
Was the disruption of Uranus, with its abnormal obliquity, linked to the Rhaetic 50o shift of Earth obliquity, to the bursting from the mantle of the great dolerite and basaltic floods, the end of the Pangean platform, and the beginning of the Tethys?
Was the disruption of Neptune linked with the 50o shift of our lithosphere obliquity in the Middle Devonian, with mantle rupture and the East Australian ophiolites and the Appalachian-Tabberabberan geosynclines?
Was the disruption of Saturn linked with the great changes between the Proterozoic and Phanerozoic, and mantle rupture with the eruption of the Tasmanian and Victorian ophiolites, or was the disruption of Jupiter correlated with Hadean events which ended the Archean and ushered in the Proterozoic'?
These are quite speculative questions, but the American satellites have opened a new door to the solar members and it is time to ask such questions, and begin the next stage of geology.
Geology began with the belief that what is, always was. Through the centuries a dramatic history of eons, eras, periods, epochs, and formations has been elucidated, with many false digressions on the way - such as the flat Earth, age limited to a few millennia, permanence of oceans and continents, creation of life, earth the center of the universe.
In my judgement, these residual ”now-always-was” beliefs have still to be abandoned - that Earth's diameter essentially as it always was, that great oceans which now cover half of the Earth, always did, that the lithosphere has always suffered great compression. Although inter-continental displacements is now established (a few knew of this from a century ago, but the many only for the last forty years). In fact, continents have not really shifted - they have remained on their foundations while oceans expanded between them (Figures 108 and 109).
All this progress has looked inward. Outward, Earth is a member of the solar system. According to common creed, Sun, Moon, planets, asteroids, meteorites, formed when Earth was born, and changed little since. What is, always was.
The time has
come to scrutinize Earth's geologic history for palimpsests of events out